ALBERT

Description: We report on the fabrication and measurement of the switching characteristics of Co/Pd multi-layer thin films and nanodots. We used the method of anomalous Hall effect to obtain the hysteresis curves of both in-plane and out-of-plane magnetization. While Co/Pd thin film is found to switch by nucleation followed by domain propagation, Co/Pd nanodots switch by quasi-coherent rotation. We found that the coercivity of Co/Pd increases by a power law with respect to decreasing dots size. The coercivity can be reduced by exchange coupling the Co/Pd multi-layer to a 2 nm thick Co layer. Adding a Cu spacer layer between the Co/Pd multi-layer and Co layer provides a reliable way to modulate the strength of exchange coupling and tailoring the coercivity. As the Cu spacer becomes thicker, the coercivity increases. The exchange energy density is estimated to be 14.6 Merg/cm 3 and the exchange constant, 2.92 erg/cm 2 . The dependence of saturation field and coercivity on the thickness of the Cu spacer layer is fitted to the same empirical model and the exchange interaction is found to decay exponentially with distance. The exchange-coupled samples switch by quasi-domain propagation for both thin films and nanodots.

Description: In the past decade, nondestructive electromagnetic techniques have been extensively used for the characterization of materials. In this paper, the relation between the microstructural/mechanical characteristics of D2 tool steel with magnetic and electrical properties and eddy current (EC) test outputs has been established. Quenched samples obtained from different austenitizing temperatures (from 1000 °C to 1130 °C) were used to investigate the effect of retained austenite, martensite, and carbides phase fraction as well as prior austenite grain size, on the electromagnetic properties such as electrical resistivity and magnetic saturation. Variations of induced voltage in the pickup coil and location of impedance point in the impedance plane as a function of austenitizing temperature were interpreted by considering the changes in magnetic saturation and electrical resistivity and their effects on the EC outputs. This paper indicated that there is a good correlation between the EC parameters and retained austenite.

Description: Magnetic flux leakage (MFL) technique is generally considered as an efficient and effective nondestructive testing method, which has been widely used in the drill pipe detection in oil field. This paper aims at studying the magnetic concentrating effect, and proposing a method of gathering the MFL by means of magnetic concentrating device. Electromagnetic finite-element analysis shows that pipe MFL signals centralize near defects obviously and the leakage signals detected by Hall elements enhance greatly as magnetic concentrating structure can collect useful magnetic component. A drill pipe MFL experiment confirms the analysis results that the probe with magnetic concentrating device could obviously improve SNR of MFL signals, increase measuring the width of defects and reduce the requirements of liftoff value. Therefore, it is of great help to improve pipe leakage flux testing sensitivity.

Description: In this paper, a novel meander–spiral coil (MSC) was designed as an eddy-current sensor (ECS) probe, which has small sensing area and spot size, nearly no limitation of mounting space, and can perform better than the regular-spiral coil (RSC). The results of the finite-element analysis show that the MSC has a magnetic active area that was only a quarter of that of the RSC. The MSC has much smaller inductance and resistance than the RSC, though the former has high sensitivity similar to the latter. These types of spiral coils were manufactured by printed circuit board technology and tested, which proves that the MSC has a small sensing range. Owing to MSC’s small magnetic active area and high performance, this type of spiral coil is suitable for applications in sensor arrays and micro-electromechanical systems. Furthermore, using the MSC, ECSs have the potential to be used for micro-gap measurement, accelerometers, and pressure measurement applications, as in the case of capacitive sensors. Moreover, ECSs are inherently immune to environmental contaminations.

Description: Multiphase brushless dc (BLDC) machines are implemented in electric and hybrid electric vehicle applications due to their high torque/power density, good fault tolerance capability, and low torque ripple. Moreover, the per-phase converter rating can be reduced by increasing the phase number. However, the number of magnetic couplings between phases increases with the phase number, and these magnetic couplings can have an important influence on the machine performance. Therefore, they need to be considered in simulation models and their effect should be considered in control algorithms. Accordingly, the objective of this paper is to analyze the effect of magnetic phase couplings on the performance of multiphase BLDC machines with an overlapping phase winding configuration. First, a detailed electric machine model, in which the machine parameters that are determined by 2-D finite-element method analysis are implemented, is developed. Using this model, the influence of mutual inductances on phase current characteristics with pulse amplitude modulation (PAM) and pulsewidth modulation (PWM) controls is investigated. In addition, a novel PAM-based control strategy, in which the effect of phase mutual inductances is considered, is proposed and analyzed. After demonstrating the influence of mutual inductances on phase current characteristics, the dependence of mutual inductances on the winding configuration is studied. Finally, experimental results with the PAM control and the new PAM-based control are used to validate the simulation results.

Description: A 2-D soft-in, soft-out equalizer consisting of multiple low-complexity constituent equalizers is proposed for the turbo equalization of 2-D intersymbol interference. The constituent equalizers are simple 1-D linear equalizers running in different directions over a 2-D array of storage cells. Simulation results as well as an extrinsic information transfer chart analysis indicate that the proposed concatenation provides performance comparable with finite-window trellis-based equalizers while requiring a much lower complexity level.

Description: In this paper, the constitutive relation of longitudinally magnetized ferrites (LMF) is simplified and transformed to an equivalent relation involving tensors with first-order dispersive components more suitable for use in the time domain analysis. Further treatment leads to a diagonal permeability tensor that yields approximating formulas to relate the magnetic field to the magnetic flux density, which allows eliminating this later and reducing the number of field variables involved. Later, a similar result is achieved using a variable transformation. This reveals that magnetized ferrites actually have a permeability tensor simpler than the Polder tensor, in addition to a permittivity tensor with first-order dispersive components, which contradicts the known theory about ferrites. Finally, it is shown that the results obtained for the LMF case could be extended to the transversely magnetized ferrite case and to the general case of arbitrary state of magnetization. Some examples are presented with numerical results to validate the proposed formulations.

Description: Provides a listing of the editors, board members, and current staff for this issue of the publication.

Description: Using electrodeposition into anodic aluminum oxide (AAO) membranes, we have successfully fabricated near-equiatomic Fe 48±3 Pd 52±3 nanowires (NWs) with the diameter of $approx 200$ nm and the length of $approx 3.5~mu{rm m}$ . X-ray diffraction and transmission electron microscopy/selected-area electron diffraction analyses revealed that the as-deposited NWs are isotropic and polycrystalline with an average crystal size of 5 nm and have an fcc crystal structure. Magnetic force microscopy (MFM) on a single Fe–Pd NW revealed its single-domain behavior with the easy axis of magnetization along the long axis of the NW. The magnetizationswitching behavior of a single Fe–Pd NW studied with the MFM suggested a square-shaped magnetization curve $(M/Ms = 1)$ with $H_{CVert} approx 3.2$ kA/m. In addition, using in-field MFM techniques, the effects of dipolar interactions in an Fe–Pd array of NWs still embedded in the AAO were determined. It was found that the dipolar interactions greatly reduce the parameters of the magnetization hysteresis loop, such as the coercivity, the remanence, and the switching-field distribution of the Fe–Pd NW array.

Description: The Technical Committee of the IEEE Magnetics Society has selected seven research topics to develop their roadmaps, where major developments should be listed alongside expected timelines: 1) hard disk drives; 2) magnetic random access memories; 3) domain-wall devices; 4) permanent magnets; 5) sensors and actuators; 6) magnetic materials; and 7) organic devices. Among them, magnetic materials for spintronic devices have been surveyed as the first exercise. In this roadmap exercise, we have targeted magnetic tunnel and spin-valve junctions as spintronic devices. These can be used, for example, as a cell for a magnetic random access memory and a spin-torque oscillator in their vertical form as well as a spin transistor and a spin Hall device in their lateral form. In these devices, the critical role of magnetic materials is to inject spin-polarized electrons efficiently into a nonmagnet. We have accordingly identified two key properties to be achieved by developing new magnetic materials for future spintronic devices: 1) half-metallicity at room temperature (RT) and 2) perpendicular anisotropy in nanoscale devices at RT. For the first property, five major magnetic materials are selected for their evaluation for future magnetic/spintronic device applications: 1) Heusler alloys; 2) ferrites; 3) rutiles; 4) perovskites; and 5) dilute magnetic semiconductors. These alloys have been reported or predicted to be half-metallic ferromagnets at RT. They possess a bandgap at the Fermi level $E_{F}$ only for its minority spins, achieving 100% spin polarization at $E_{F}$ . We have also evaluated $text{L1}_{0}$ alloys and $D0_{22}$ –Mn alloys for the development of a perpendicula- ly anisotropic ferromagnet with large spin polarization. We have listed several key milestones for each material on their functionality improvements, property achievements, device implementations, and interdisciplinary applications within 35 years time scale. The individual analyses and the projections are discussed in the following sections.

Description: Perpendicular magnetic recording (PMR) in the hard disk drive is approaching its physical limits. In an earlier work, the dedicated servo (DS) recording system has been proposed to provide continuous position error signal for servo, enable higher servo sampling rate, and improve the overall servo performance. A further benefit is that the DS layer results in surface area savings at the data layer. However, it was also reported that the embedded servo layer introduces baseline variation and non-linear transition shift (NLTS) to the readback signal of the data layer. In this paper, we propose novel signal processing techniques to improve the bit error rate (BER) in DS recording. The synchronous averaging technique is proposed to improve the BER in the presence of baseline variation distortions. Further, the servo and data-dependent noise prediction method is proposed to mitigate the effect of the NLTS. Through the use of these techniques the linear density loss from the conventional PMR media is reduced.

Description: This paper presents a method that has been developed to determine the quantity of accumulated magnetic particles in mice tissues using magnetization measurements. Dispersions of platelet Fe 3 O 4 particles with the size of 30–50 nm and a saturation magnetization of $sim 80$ Am 2 /kg were intravenously administered to mice. Primary tissues were dried to measure the magnetization. The amounts of Fe 3 O 4 particles accumulated in the tissues were obtained by dividing the magnetization of tissues by the magnetization of Fe 3 O 4 particles under a magnetic field of 39.8 kA/m. A remarkable accumulation of particles was observed in the liver and the spleen, being supported by the observation of tissues using Prussian blue staining. Total Fe 3 O 4 particles accumulated in primary tissues were $sim 38$ –40 and 40–44 wt% against the particles in administered dispersions with 3 and 0.4 wt% contents, respectively. The method developed in this paper is considered to be effective for verifying magnetic hyperthermia and thermoablation therapies, in which the quantity of accumulated particles directly reflects the heating power required for those therapies.

Description: Self-ordered arrays of Ni, Ni(50)Pd(50), and Ni(78)Pd(22) nanowires were synthesized by simultaneous electrochemical deposition of Ni and Pd components into porous templates of anodic aluminum oxide using alternating current. This paper is focused on the interplay of structure and chemical composition of Ni and Ni–Pd bicomponent nanowires arrays and the peculiarities of its magnetic anisotropy.

Description: Most investigations of all spin logic (ASL) have been based on the monodomain approximation of magnetization switching. The sensitive and stochastic nature of spin transfer torque (STT) switching creates pressing requirements for analyzing ASL from a micromagnetic perspective also. Hence, in this paper, ASL is studied from a micromagnetic perspective by developing a simulation framework that can capture diffusive spin transport. The spin transport model is calibrated from the existing experimental results on nonlocal spin valve measurements. Then, using this framework, STT switching is studied for input–output nanomagnets with in-plane and perpendicular magnetic anisotropy for ASL devices (ASLDs). Precisely defined architecture and design constraints for such input–output nanomagnets are presented. Further, a previously proposed switching mechanism by driving the nanomagnet into a metastable state is also incorporated into micromagnetic framework. Using the aforementioned mechanism, the critical current required for STT switching can be reduced to as low as 20 $mu $ A. Moreover, the graphene channel ASLD using tunnel contact at the injector is demonstrated for copy and invert logic operations.

Description: We present coupled spin torque nano oscillators (STNOs) as electronic neurons for efficient brain-inspired computation. The coupled STNOs show two distinct outputs, depending on whether the frequencies are locked or not. The locking mechanisms are based on magnetic coupling or injection locking. The neuron firing threshold can be set by tuning the locking range of the coupled STNOs. We employ a crossbar array of programmable memory devices like memristors to implement electronic synapses that work seamlessly with the coupled STNOs for hardware implementation of neural networks. Results show that injection locking-based neuron model can be attractive from scaling point of view and computation like character recognition can be performed with energy consumption per neuron of $sim $ 1.8X and $sim $ 3X lower than the digital and the analog CMOS counterpart, respectively.

Description: With the train’s speed improving, and running interval time decreasing, traditional rail defect inspection methods cannot meet the efficiency requirement of railway industrial standards. In this paper, we propose a new online rail defect inspection method which is using electromagnetic tomography (EMT) technique. The method uses the tomographic approach to measure the alternating magnetic signal modulated by cracks in the rail and then reconstruct the distribution of cracks. The difference to common eddy-current rail defect inspection is, that the EMT can acquire the defect shape and position information. The sensor and signal processing hardware of the EMT rail defect inspection system can be installed on the common passenger or freight train. This solution allows continuous inspection, and therefore reduces the critical accident events caused by rail defect. A model is designed and the forward problem of the model is calculated using electromagnetic finite-element method. Rail defect reconstruction simulations are done using linear backprojection and Tikhonov regularization algorithm to verify the principle of this method. Furthermore, an experimental system is built to simulate the rail defect. The laboratory experiment results show that the electromagnetic rail defect inspection is a feasible approach for reconstruction of the shape and position information of rail defect.

Description: This paper provides the 3-D time-dependent analytical solution of the electromagnetic fields and forces emerging if a coil or a permanent magnet moves with a sinusoidal velocity profile relative to a conducting slab of finite thickness. The results can be readily used in application scenarios related to electromagnetic damping, eddy current braking, energy harvesting, or nondestructive testing in order to efficiently analyze diffusion and advection processes in case of harmonic motion. This paper is performed for rectangular and circular coils as well as for cuboidal and cylindrical permanent magnets. The back reaction of the conductor and therewith associated inductive effects are considered. The solutions of the governing equations and the integral expressions for the time-dependent drag and lift force are provided. The analytical results are verified by a comparison with numerical simulations obtained by the finite-element method. The relative difference between the analytically and numerically evaluated force profiles was <0.1%. Exemplary calculations show that the waveforms of both force components strongly depend on the level of constant nominal velocity $v_{0}$ , the magnitude of the velocity oscillation amplitude $v_{1}$ , and the underlying oscillation frequency $f_{v}$ .

Description: Provides a listing of board members, committee members and society officers.

Description: The mechanism and the influence of the on-load terminal phase voltage distortion by the armature reaction in interior permanent magnet (IPM) machines with fractional-slot concentrated windings (FSCWs) are investigated in this paper, by taking a 12-slot/8-pole machine as an example. The phenomenon is presented first, which shows that the peak voltage will be much higher than the fundamental value, especially under the flux-weakening operation. Then, the mechanism is investigated with the aid of the frozen permeability method. Due to the geometric feature of the FSCW IPM rotor, the armature reaction flux will asymmetrically enhance the local magnetic saturation in the tooth-tips and the rotor lamination region near the rotor ribs, which disrupt the smooth variation of phase flux linkage and lead to a voltage distortion. With the increasing of current advancing angle ( $beta $ ), this effect will become more obvious and result in the higher distortion level. Furthermore, the influences of voltage distortion on the machine torque performance are investigated, which show that it will only contribute to the torque ripple in the constant torque region, but will largely reduce the flux-weakening operation region compared with the ideal one calculated by the fundamental voltages only. Finally, a prototype is manufactured and tested to validate the analyses.

Description: A typical giant magnetostrictive actuator (GMA) expands a magnetostrictive rod to generate strain by varying the current in the coil that surrounds the magnetostrictive rod. The heat generated by the current deteriorates the GMA performance. In particular, a constant current in the coil is required to produce the desired magnetic field when an output strain should be maintained. The GMA does not produce any mechanical power in this condition, but constant power is being consumed by the excitation coil. This paper presents a new type of motor-driven GMA (MDGMA), which works in a coil-free driven manner. The magnetic field in the iron–gallium alloy (Galfenol), which is a type of magnetostrictive material, is periodically altered by rotating the permanent magnets instead of varying the coil current in the traditional GMA. The proposed MDGMA not only achieves continuous adjustment of the output strain, but can also maintain a constant output strain without consuming any power. In addition, the coil-free design releases the new MDGMA from the heat generated by the excitation coil, which allows the MDGMA to work more stably.

Description: This paper presents a 3-D analytical model for axial-flux eddy-current couplings and brakes, leading to closed-form expressions for the torque and the axial force. The proposed model is valid under a steady-state condition (constant speed operation). It takes into account the reaction field due to induced currents in the moving conducting part. In order to simplify the analysis, we adopt the assumption of linearization at the mean radius, and the problem is then solved in 3-D Cartesian coordinates (curvature effects are neglected). The solution is obtained by solving the Maxwell equations with a magnetic scalar potential formulation in the nonconductive regions (magnets and air gap) and a magnetic field strength formulation in the conductive region (copper). Magnetic field distribution, axial force, and torque computed with the 3-D analytical model are compared with those obtained from the 3-D finite-element simulations and experimental results.

Description: On behalf of the Publication Committee of the IEEE International Magnetic Conference (Intermag 2015), I am pleased to present a selection of papers from Intermag 2015 held at the China National Convention Center, Beijing, China, on May 11-15, 2015. Among the 1759 oral and poster presentations in Intermag 2015, 1076 papers were submitted for a peer review and possible publication in the present volume of the IEEE TRANSACTIONS ON MAGNETICS, covering various aspects of magnetic materials and devices. After a rigorous review process, 590 manuscripts were selected for publication in this issue of the Transactions, strictly following the IEEE rules for conference-related papers.

Description: A series of orthorhombic perovskite Sm 1– x Tb x FeO 3 ( $x$ = 0, 0.3, 0.35, 0.4, 0.45, and 0.5) powder was readily prepared by sol–gel combustion process. The Tb-doping effects on the structure, morphology, and magnetic properties of SmFeO 3 have been studied in detail. Pure phase SmFeO 3 was obtained when calcinated at 900 °C for 3 h. By Tb doping, the synthesis temperature of orthorhombic perovskite-type Sm 1– x Tb x FeO 3 powder increased to 1100 °C. Moreover, the ferromagnetic (FM) interactions within the system are effectively enhanced, while the anti-FM coupling is greatly weakened, which is ascribed to the exchange coupling between Tb and Fe ions.

Description: On behalf of the Organizing Committee of the International Magnetics Conference 2015 (Intermag 2015), it is our pleasure to present this issue of the IEEE T ransactions on M agnetics comprising selected papers from Intermag 2015. These categories this year included: Magnetic Recording, Spintronics and Applications, Sensor/MEMS or RF Materials and Devices, Electric Machines and Power Devices, Life Sciences and Applications, Magnetic Thin Film and Nanostructures, Functional Magnetic Materials, Soft Magnetic Materials, Permanent Magnet Materials, and Microscopy Imaging and Characterization.

Description: Provides a listing of the editors, board members, and current staff for this issue of the publication.

Description: In shingled magnetic recording, the multihead multitrack (MHMT) detector can better combat the effect of intertrack interference than the single-head single-track detector. Such a detector, however, has prohibitive implementation complexity. In this paper, we propose to use the reduced-state sequence estimation algorithm to significantly reduce the complexity, and render MHMT practical. A commonly used symmetric two-head two-track channel model is considered in this paper. Well-structured reduced-state trellises are constructed by evaluating the effective symbol pair distances and designing proper set partitioning principles. Different trellis configurations are obtained based on the desired performance/complexity tradeoff. Simulation results show that the MHMT detector can achieve near maximum-likelihood performance with a small fraction of the original number of trellis states.

Description: 2-D magnetic recording (TDMR) exploits 2-D signal processing using the waveforms reproduced by array head from the intended and adjacent tracks to mitigate the effects of intertrack interference. However, an array head has the issue on the degradation of bit error rate (BER) performance due to head skew. In this paper, we evaluate the BER performance of TDMR R/W channel with head skew under a specification of 4 Tbit/in $^{2}$ employing low-density parity check coding and iterative decoding system using a 2-D finite-impulse response filter by computer simulation. The results show that our system can achieve the reliable BER performances by appropriately setting the reader scanning positions at the head skew angle between 0° and 3°.

Description: Simulations of shingled, microwave-assisted magnetic recording were carried out. First, a simplified model of the head field near the corner of the main pole of a write head was used to understand the effect of the spin torque oscillator (STO) position relative to the head. Next, shingled tracks were written and evaluated for two different write head and STO geometries. For shingled recording, locating a rotated STO on the side of the main pole may provide some advantages in that medium grains experience the high-frequency (HF) field for a longer time and the chirality of the HF field does not change as the grains pass by the STO. Recording simulations show that the rotated STO writes smoother track edges at lower densities, but there is little difference in signal-to-noise ratio at high linear densities.

Description: In heat-assisted magnetic recording (HAMR), a higher recording density is pursued. Short-pulse laser heating is a good way to improve the thermal distribution in the media and to reach the full potential of recording density for the HAMR technology. In this paper, the effects of short-pulse laser qualities, such as pulse frequency deviation, pulse power deviation, and pulsewidth deviation, on recording performances for the HAMR with 100 ps pulse laser heating have been analyzed by simulation. The results indicated that the frequency jitter has the most significant effect on the recording performance among these three parameters. The decreases of signal-to-noise ratio (SNR) for 6% deviations of pulse frequency, pulse power, and pulsewidth are 5, 2, and 1.5 dB, respectively. A certain degree phase delay of pulse laser related to magnetic field switching time is beneficial to reducing the effect of pulse frequency deviation on SNR. When the phase delay changes from 0° to 180°, an SNR improvement of $sim 2$ dB is obtained. The measurement result of a real laser diode output (pulsewidth of 97 ps and pulse frequency of 2 GHz) by gain-switching technology presents a very low frequency deviation (<0.5%). It indicates that the gain-switching technology is a suitable approach for a short-pulse laser generation for the HAMR application.

Description: A timing recovery method for a high-density tape storage system is studied in this paper. Since tape systems suffer from large speed variations compared with disk systems, the design of a stable timing recovery scheme that can operate under low signal-to-noise ratio (SNR) conditions is important. In such low SNR scenarios, decision errors made by the detector occasionally cause the phase-locked loop circuit to lose track of the correct signal, which is often called the loss-of-lock (LOL) phenomenon. In order to mitigate the LOL issue, soft information from the Viterbi detector is utilized. It is clarified that the negative effect of unreliable decisions from the detector can be compensated for by dynamically controlling the feedback gain of the timing recovery loop as a function of decision reliability. It is shown that the LOL rate performance can be improved by this approach, with only a minor increase in the implementation complexity.

Description: The permeability of the magnetic soft underlayer (SUL) was systematically varied by changing the antiferromagnetic exchange coupling, and the effect on recording performance and adjacent track erasure (ATE) and far track erasure (FTE) was investigated. Perpendicular magnetic recording performance highly depends on SUL permeability. Highly permeable SUL can reduce the head erasure field located at far tracks from a stressing track but generates more erasure at adjacent tracks near the side shield. Optimum SUL permeability can improve on-track performance with tolerable ATE or FTE. Finite element method models of a shielded write head and media with different SUL permeabilities were performed. A high-permeability SUL has a larger impact on short-time high FTE fields and potentially affects the erasure at 3–6 tracks from main pole. This shows agreement with experimental results.

Description: In this paper, we develop a portable dynamic switching model for perpendicular magnetic tunnel junctions (MTJs) considering both thermal fluctuation and process variations. The model uses macro-spin approximations where the free layer (FL) of MTJ is assumed to be in a single-domain structure. The model can generate dynamic switching transience curves at different current densities and simulate the switching successful rates for the given pulse lengths at different current densities. We also use the model to study the impact of temperature and device process variations on the switching performance, such as switching time variations. It is shown that the temperature effect is not significant when the switching current is relatively larger, and hence the spin current effect is strong enough to overtake the temperature effect. As for the process variations, it is shown that the FL thickness has a more significant effect on the switching time than the size of the FL does.

Description: We investigate the transport property of the surface states of a topological insulator (TI) in the presence of a time-dependent potential. We find that the normally incident electrons can be perfectly transmitted through the time-dependent region under symmetrical potential configuration. But the perfect transmission is broken upon application of an asymmetrical potential. The contour plot of the transmission shows a fishlike transmission profile, which varies according to the potential configuration, and the strength and frequency of the time-dependent potential. This distinct transmission characteristic may be utilized to modulate the transport property of the TI.

Description: Superparamagnetic tunnel junctions (SMTJs) are noise powered stochastic oscillators, which can harness thermal energy through phenomena such as stochastic resonance and noise-induced synchronization. This enables them to operate with the minimal externally supplied energy, and therefore, makes them promising candidates for implementing bioinspired computing schemes. These applications require understanding how SMTJs can be integrated into CMOS circuits. In this paper, we present a compact model of SMTJ, written in the VerilogA language, that can be used within standard integrated circuit design tools. This compact model is based on the Néel–Brown model and allows for fast simulations. We show that this model can reproduce the experimental characterization of a sample subjected to different values of dc currents. Then, we definitively demonstrate the validity of the model by confronting it to the experimental results in the case of a complex phenomenon: noise-induced synchronization.

Description: Spin–orbit torque generated by spin-torque interaction provides a new writing mechanism for spintronic devices. This paper investigates spintronic memory devices for match-in-space, content addressable, and self-reference applications, utilizing spin–orbit torque generated by spin-torque interaction combined with the conventional spin torque generated by magnetization polarization. New system and device solutions are proposed for targeting different spintronic technology development stages. These proposals include spin content addressable memory (CAM) structure of DRAM cell with embedded MRAM, dual spin Hall magnetic tunneling junction CAM device, and spin-orbitronics memory device, capable of multi-bit match-in-space and single-bit nondestructive self-reference functionality.

Description: We study a wireless communication system based on a magnetic tunnel junction spin-torque nano-oscillator (STNO) by employing amplitude-shift-keying modulation. By varying the pulse modulation frequency ( $f_{m}$ ) from 1 kHz to 2 MHz and distance ( $D$ ) between the antenna from 25 to 150 cm, we show a maximum data rate of 6 Mb/s (at $D=25$ cm and $f_{m}=1$ MHz), a limit imposed by our setup and noise generated by the STNO itself. We also report the average amplitude noise ( $S_{delta a}$ ) and average white frequency noise ( $S_{rm wh}$ ) of the wireless communication system and discuss their dependence on the distance between the antennas.

Description: We report a novel spin-torque diode (STD) radio-frequency detector by utilizing tilted fixed-layer magnetization and in-plane free-layer magnetization. Through macrospin modeling and numerical simulation, we study both the direct current (dc) dependence and the perpendicular external field dependence of the output voltage of the detector. We systematically investigate both the fixed-layer magnetization tilt angle dependence and the dc dependence of the resonance detection regime of the detector. It is found that an ultrawide resonance detection regime 6.5 GHz can be achieved, which is 1200% higher than the traditional STD magnetic tunnel junction detector with in-plane fixed-layer magnetization.

Description: Perpendicular-anisotropy magnetic tunnel junction (MTJ) is one of the most promising candidates to build hybrid logic-in-memory architecture, because of its nonvolatility, infinite endurance, and 3-D integration with a CMOS technology. A novel magnetic full-adder (MFA) based on this architecture is proposed, with MTJs switched by spin-Hall-assisted spin-transfer torque (STT). Owing to the assistance of spin-Hall effect (SHE), MTJ switching time can significantly be reduced, and high operation frequency can be achieved. Moreover, the endurance of oxide barrier is largely enhanced as the requirement of lower write voltage. Using an industrial CMOS 28 nm design kit and a physics-based three-terminal spin-Hall-assisted STT-MTJ model, functionality and performance of the proposed MFA have been simulated and validated. A 1 ns STT current pulse assisted by 0.35 ns SHE current pulse is sufficient to switch the MTJ configuration. When compared with the previous MFAs based on STT-MTJ, the proposed MFA achieves 38% less operation time and 31% less power consumption to perform read and write operations.

Description: DC magnetization, electrical transport, and magnetoresistance (MR) measurements of Fe 1– x Co x Si single crystals with $x approx $ 0.7–0.3 are reported. Fe 1– x Co x Si series presents a typical Stoner band excitation characteristic in the field-dependent magnetization profile. Co-doping ( x > 0.3) in the Fe 1– x Co x Si compound shows a semiconductor–to–metal transition. Enhanced positive MR has been observed when $sim$ 1/3 of the Fe was substituted with Co, which suggests that the spin density of states in the minor band (semiconductor characteristic) dominates the electronic properties.

Description: The magnetic properties of $3d$ transition metal ( ${mathrm{ TM}}={mathrm{ V}}$ , Cr, and Mn)-doped ZnO nanowires (NWs) with and without oxygen vacancy are investigated by ab initio calculations. The magnetic moments can be induced by TM impurities in ZnO NWs, localized on the $3d$ TM atoms and their neighboring O atoms. Furthermore, the ferromagnetism in V-, Cr-, and Mn-doped ZnO NWs is strongly correlated with oxygen vacancies.

Description: The polycrystalline Ba 3– x Sr x Co 2 Fe 24 O 41 ( $x = 0.0, 0.5, 1.0$ , and 1.5) samples were synthesized by the solid-state reaction method. The crystalline structure of the samples was found to be a hexagonal structure with a space group of $P6_{3}/mmc$ . The lattice constants $a_{0}$ , $c_{0}$ , and $V_{u}$ of the samples decrease with increasing Sr concentration. From the field-dependent hysteresis curves under 10 kOe at 295 K, the values of $M_{s}$ increase while the values of $H_{c}$ decrease. The zero-field-cooled magnetization curves under 100 Oe between 4.2 and 300 K show the spin transition, and the value of $T_{s}$ decreases from 230 K for $x=0.0$ to 135 K for $x = 1.5$ with increasing Sr concentration due to the reduction of planar anisotropy with the difference in ionic radius between Ba 2+ and Sr 2+ ions. From the isomer shift value ( $delta $ ) obtained from Mössbauer spectra, the charge states of all samples are determined to be Fe 3+ high spin state. With increasing Sr concentration, the reduction of hyperfine field $langle H_{mathrm {hf}}rangle $ suggests the change in hyperfine interaction between Fe ions because of the larger ionic radius of Ba 2+ ion than that of Sr 2+ ion, leading to decreasing $M_{s}$ .

Description: The effects of silicide formation on the surface structure and magnetic properties of Co thin films on Si (100) were investigated. Annealing temperature significantly changed the formation of silicide. CoSi phase was formed during annealing at 600 °C and 700 °C. CoSi 2 phase was formed during annealing at 800 °C. The anisotropy of Co/Si (100) films changed due to the formation of silicide. In addition, both the particle size and the surface roughness increased with the increase of annealing temperature, which led to the increase of coercivity up to 700 °C. However, the better crystallinity $ {H_{C}}$ decreased at 800 °C.

Description: Alloy composition (Co 94 Fe 6 ) 72.75 Si 12.25 B 13.25 Cr 1.75 was designed to develop nearly zero-magnetostrictive materials in the form of ribbons and wires to obtain suitable magnetic properties for use as giant magnetoimpedance (GMI) and low-noise fluxgate sensor cores. During the development of magnetic sensing core using amorphous wires of diameter 80 $mu text{m}$ for GMI sensing, we observed a maximum impedance change (GMI ratio) of 430% with as-cast wires, which further enhanced to 650% when annealed at 300 °C for 5 min. The effect of annealing temperature and stress on the magnetic properties of fluxgate sensing core materials has been studied. Magnetic hysteresis loops were measured with 3-mm-wide and 45- $mu text{m}$ -thick amorphous ribbons on a toroidal ring of 50 mm diameter for fluxgate sensor core. A coercivity of 10.57 A/m and saturation field of $sim$ 150 A/m were observed with as-quenched ribbon, which improved to a coercivity of 2.16 A/m and saturation field $sim$ 100 A/m when annealed without stress just above its Curie temperature. An induced anisotropy transverse to excitation direction was achieved by applying temperature with stress and time (300 °C/ 100 MPa/ 20 min) to use it for fluxgate sensor core.

Description: The change in the lancet domains of grain-oriented steels in the range from the room temperature (RT) to far above the Curie temperature ( $T_{c}$ ) was investigated using the domain observations by the photoemission electron microscopy combined with X-ray magnetic circular dichroism and the domain theory. Lancet domains were observed to be annihilated at the temperature below $T_{c}$ , with 180° basic domains occurring. The minimization of the magnetic free energy considering the intrinsic physical constants as the functions of the temperature enabled us to quantitatively explain the observed temperature dependence of lancet domains. The present model revealed that the temperature dependence of the cubic anisotropic constant greatly contributes to the annihilation of lancet domains at the temperature below $T_{c}$ . The improvement of the crystal misorientation, the thinner thickness, and the enhancement of the tensile stress applied to the steels are predicted to reduce the annihilation temperature of lancet domains. The tensile stress required to annihilate lancet domains at 200 °C is predicted to allow approximately half the stress to annihilate them at RT.

Description: We report investigations on temperature-induced transformation of magnetic domain structures in the Fe-rich amorphous glass-covered microwires. The images of domain structures and magnetization reversal process were registered by means of magnetooptical Kerr microscopy. The coexistence of two different types of surface domain structures with helical magnetization components has been found. The obtained results discussed in the frame of the model supposed the stress influence on the domain structure.

Description: NiZn ferrites with different amounts of CuO have been synthesized by the conventional ceramic method and their spectra of complex permeability were investigated. The CuO contents affect the grain size and microstructure of NiZn ferrite obviously, which also result in the variation of saturation magnetization, magnetocrystalline anisotropy, and porosity. Along with these relevant magnetic properties, the superposition of magnetizing mechanisms was testified to be predominant in determining the value of permeability. To manifest the increase of initial permeability, the permeability spectra of NiZn ferrite were resolved into two components, including domain wall movement and spin rotation magnetization. The fitting results show that, with the increasing amounts of CuO, the dominant contribution to dynamic magnetization changes from spin rotation magnetization mechanism to domain wall movement.

Description: Fe-based soft magnetic composites (SMCs) with high $B_{s}$ and low core loss were fabricated by acidic bluing coating. Effects of reaction time and annealing temperature on the magnetic properties of the SMCs have been investigated. The Fe 3 O 4 grows as the coating layer of the Fe powders and converts to Fe 2 O 3 with increased reaction time. The iron oxide coating layer gives rise to highly normalized saturation magnetization (0.954–0.928) and low core loss due to its high electrical resistivity. The lowest core loss (785.1 mW/cm 3 measured at 50 mT and 100 kHz) of the Fe SMCs can be achieved with the reaction time of 30 min and annealing temperature of 550 °C.

Description: In general, the contribution to the reinforcement of the magnetism in the order–disorder transition of FeAl alloys depends on their Fe content and the order–disorder transition. However, the Fe 75 Si 15 Al 10 alloys were investigated by means of first-principles calculation and experimental verification. We found that the mechanism of the magnetic moment ( $mu _{m}$ ) reinforcement is the exchange interaction of Fe atom with its nearest neighbor Fe atoms. In addition, the exchange interaction of Fe–Fe atoms is affected by internal stress, lattice distortion, the Fe content, and the position of nearest neighbor nonferrous atoms (Si and Al atoms). At the annealing temperature of 600 °C , the $mu _{m}$ is the maximum value, as the ordered DO3 structure is transformed extremely.

Description: A 0.23 mm thick grain-oriented silicon steel sheet was successfully produced based on strip casting and two-stage cold rolling route. The evolutions of microstructure and texture along the complete processing route were briefly investigated. It was shown that the as-cast strip was composed of coarse ferrite grains and martensite, and the texture was mainly characterized by strong {001} $langle 0vwrangle $ texture. Goss texture was absent in the hot-rolled strip, which was distinct from the well accepted results that Goss texture had its origin during hot rolling. After the cycle of the first-stage cold rolling, an intermediate annealing, the second-stage cold rolling, and a primary annealing, the strip exhibited a fully recrystallized microstructure with a weak $alpha $ -fiber texture and a relatively strong $gamma $ -fiber texture. Goss texture was not observed through the thickness of the primary annealed strip. This was significantly different from the previous results that Goss texture was the most populous component in the primary recrystallization texture of two-stage route in conventional process. After secondary recrystalization annealing, the magnetic induction $B_{8}$ of the sheet was as high as 1.84 T.

Description: The BaCo 2− x Zn x Fe 16 O 27 ( x = 0, 0.5, 1) samples were prepared by solid-state reaction method. The prepared samples are single-phased, and their crystal structures are determined to be hexagonal with a space group of P6 3 /mmc from Rietveld refinement analysis. The magnetic saturation values were increasing, and the values of coercivity were decreasing with increasing Zn contents. The experimentally measured temperature dependence of magnetization curves shows magnetic transitions. We have measured Mössbauer spectroscopy at various temperatures to investigate microscopic magnetic properties. We analyze the obtained spectra with the five magnetic sites of $4f_{mathrm {VI}}$ , $6g$ + $4f_{mathrm {VI}}$ , $4e_{mathrm {IV}}$ , + $4f_{mathrm {IV}}$ , $12k_{mathrm {VI}}$ , and $2d_{mathrm {V}}$ . In addition, from the Mössbauer spectra, we notice the changes in the magnetic hyperfine field and electric quadrupole shift. The substituted Zn 2+ ions are located at tetrahedral site, and increase the $M_{s}$ . Curie temperatures were determined from zero-field-cooled magnetizations measurement.

Description: This paper proposed a temperature-dependent iron loss model and corresponding dynamic hysteresis model, where temperature coefficient ${k}$ is introduced to consider the thermal effect on eddy-current loss. The iron loss model is validated by massive experimental measurement of test samples, 1174 combinations of various temperatures, magnetic inductions, and frequencies for nonoriented silicon steel specimen. The relative error of the model is $sim 11$ % in a wide range of 50–400 Hz, 26 °C–200 °C, and 0–2 T. The proposed method can be applicable to other types of magnetic materials as long as whose resistivity rate exhibits approximately linear thermal dependence within a temperature range of 26 °C–200 °C.

Description: We have studied a NANOPERM-type Fe 76 Mo 8 Cu 1 B 15 metallic glass with emphasis upon its magnetic properties at low temperatures. Temperature evolution of magnetization measured under zero-field cooling and field cooling conditions upon samples with different amounts of nanocrystalline grains have unveiled a two-phase behavior in temperature range from 50 up to about 200 K. In order to understand the correlation between the structural arrangement and resulting magnetic properties, we have employed a local probe method of 57 Fe Mössbauer spectrometry performed at 300 and 4.2 K. The latter experiments were also accomplished in an external magnetic field of 6 T. Magnetically distinct regions were unveiled in the amorphous structure of the as-quenched and annealed samples. They are demonstrated by the distributions of hyperfine magnetic fields.

Description: We studied giant magnetoimpedance (GMI) effect and magnetic properties of various Co-rich amorphous microwires. We measured the values of magnetic field dependence of the GMI ratio up to gigahertz frequency range, and observed quite high GMI ratio in as-prepared Co-rich microwires even at gigahertz frequencies. We observed the different values of the magnetic anisotropy field obtained from the hysteresis loops and the impedance curves. Observed dependence can be explained considering different magnetic anisotropy in the surface layers and in the inner part of metallic nucleus and skin depth effect. Features of high-frequency GMI effect have been analyzed using ferromagnetic resonance-like approximation.

Description: In this paper, soft magnetic Mn–Zn ferrite samples have been prepared through oxide processes. The magnetic properties and the phase structures were investigated. It was found that the optimal sintering temperature is about 1360 °C. The initial permeability of the samples is 1700–2300, Curie temperature $T_{c}$ is about 140 °C−180 °C, and cutoff frequency fr is about 1 MHz. Moreover, the initial permeability of the samples is relatively stable, and its temperature coefficient is $sim 10^{-6}$ /°C at the temperature range of 20 °C−60 °C. High-frequency simulation results show that the Mn–Zn ferrites samples are suitable for the application of the wireless sensor networks in theory.

Description: We describe the enhancement of coercivity of Nd-Fe-B ultrafine powders by the grain boundary diffusion (GBD) process. An effective method for increasing coercivity in Nd-Fe-B sintered magnets is the refinement of the Nd 2 Fe 14 B grains. We decreased the powder size of the grains to <1 $mu$ m by combining hydrogenation-disproportionation-desorption-recombination, hydrogen decrepitation, and helium jet milling (He-JM). The powder size was comparable with the single-domain size of Nd 2 Fe 14 B. However, the coercivity of the ultrafine powders was lower than the value expected from their powder size, which was due to the decrease in the Nd content of the powders and lack of the Nd-rich phase on the powder surface. We performed the GBD process at 700 °C for 30 min before He-JM to increase the amount of Nd-rich phase on the powder surface. The powder showed a high coercivity of $mu_{0}{rm H}_{cJ} = 2$ T after annealing at 600 °C for 30 min. Therefore, the GBD process is an effective method for increasing the coercivity of ultrafine He-JM powders. The process increases the amount of the Nd-rich phase on the powder surface, which is converted to the liquid phase by annealing, and reduces the number of sites for reverse domain nucleation.

Description: Motivated by the wide application of the antiferromagnetic/ferromagnetic (FM) bilayer structures in high-frequency microwave magnetic devices, the Si/NiO/Ni 81 Fe 19 films with different orientations of NiO buffer layer are deposited by magnetron sputtering technology. The phase, microstructure, hysteresis loop, and angular dependence of FM resonance (FMR) linewidth are investigated by X-ray diffractometer, field-emission scanning electron microscope, atomic force microscope, vibrating sample magnetometer, and electron spin resonance spectrometer, respectively. The Si/NiO(220) film has much smaller grain size than that of Si/NiO(200) film, which is beneficial to grow a high quality NiFe film on Si/NiO(220)/NiFe bilayer structures. The hysteresis loop of Si/NiO(220)/NiFe films shows an obvious exchange bias and a relatively smaller coercivity. The FMR linewidth ( $Delta {H}$ ) of Si/NiO(220)/NiFe films is much smaller than that of Si/NiO(200)/NiFe films, which is caused by the different structural properties and morphologies of the NiO buffer layer. The Landé $g$ factors and effective damping parameters $alpha_{rm eff}$ are also discussed.

Description: In this paper, we report that W/Fe/W (001) epitaxial trilayer films exhibit very large negative uniaxial magnetic anisotropy $K_{u}$ . The magnitude of $K_{u}$ increases with decreasing the Fe layer thickness and also exhibits significant temperature dependence varying from $-2.1 times 10^{7}$ erg/cc at 300 K to $-3.5 times 10^{7}$ erg/cc at 10 K for the Fe layer thickness of 0.5 nm. The large negative $K_{u}$ is attributable to interface magnetic anisotropy in nature at the W/Fe interface and can be quantitatively reproduced by the firstprinciples calculation. The X-ray magnetic circular dichroism measurement at room temperature has revealed that the interfacial W atom is polarized in antiparallel with the magnetic moment of Fe. The induced magnetic moment of the interfacial W is almost the half of the values obtained by the first-principles calculation and the previous experiment at low temperature. This small induced W moment may be ascribed to the significant temperature dependence of the negative $K_{u}$ .

Description: A 25 nm Fe 0.7 Co 0.3 –B film was deposited by a composition gradient sputtering (CGS) method with a gradient B composition (named CGS-FeCoB). The CGS-FeCoB film showed a well-defined uniaxial magnetic anisotropy with anisotropy field H K of 400 Oe and ferromagnetic resonance frequency $f_{mathrm {FMR}}$ of 6.45 GHz. A (CGS-FeCoB/MgO) 6 multilayer was laminated by six CGS-FeCoB sublayers separated by 2 Å MgO spacers with the easy-axis direction of the neighboring CGS-FeCoB sublayers clockwise rotating 30° in turn. It is exciting that a quasi-magnetic isotropy with a quasi-isotropic hysteresis loop and omnidirectional ferromagnetic resonance around 4.77 GHz was achieved in the designed multilayer. This quasi-isotropic multilayer is promising for the application in inductors, since 100% hard-axis excitation can be achieved for inductors of any shape.

Description: The effect of strain and stain rate on microstructure and the magnetic properties of Nd–Fe–B magnets during hot-deformation process have been studied with commercial melt-spun flakes with a composition of Nd 13.6 Fe 73.6 Co 6.6 Ga 0.6 B 5.6 . The compacts produced by hot pressing at 700 °C under 100 MPa in vacuum were subjected to die upsetting at 700 °C with different deformation conditions of strain rate 0.1–0.001 $text{s}^{mathrm {-1}}$ and height reduction 40%–75%. The remanence and coercivity tended to increase and decrease with increasing strain, respectively. At below the strain of 0.5, the remanence increased more quickly with decreasing the strain rate, but the tendency was gradually reversed with increasing the strain. This was because the prolonged deformation induced the squeeze-out of Nd-rich phase from grain boundaries and the formation of coarse Nd-rich phase. In addition, the sample subjected to the prolonged deformation had quite thin and discontinuous grain boundary phase, which resulted in the decrease of the coercivity.

Description: The magnetic influence of silicon, boron, phosphorous, niobium, as well as Cu in Fe-rich amorphous was studied through ab initio molecular dynamics simulations. The small concentration of metalloids with large electronegativity is beneficial to the saturation magnetization of Fe-rich amorphous alloys, but may reduce the magnetization by p–d orbital hybridization with a large amount of inclusion. On the other hand, owing to their low electronegativity, early transition metals may bring excess electrons to the alloys system and reduce the effect of Fe electron absorption by boron or phosphorous; therefore, the inclusion of them will significantly reduce the magnetization of the alloy. The minor inclusion of Cu slightly exhibits negatively charged in Fe-rich amorphous alloys, which indicates that the transition metals with low electron losing tendency are acceptable in the alloy to maintain excellent soft magnetic properties with high magnetization.

Description: Magnetostrictive behaviors of Fe 100− x B x (001), $x=0$ , 5, and 13 at. %, single-crystal films are studied in comparison with those of poly-crystal Fe–B films under rotating magnetic fields. The output waveform of poly-crystal Fe–B film is sinusoidal and the saturation magnetostriction, $lambda _{s}$ , varies from negative to positive with increasing the B composition, $x$ , from 0 to 13 at. %. On the other hand, the output waveform of single-crystal Fe–B film is bathtub-like when measured along the easy magnetization axis of bcc[100], while it changes to triangular when measured along the hard magnetization axis of bcc[110]. The output waveform is strongly influenced by the magnetocrystalline anisotropy under a magnetic field of 1 kOe which is larger than the anisotropy field of the material. Variations of $lambda _{{mathbf {100}}}$ and $lambda _{{mathbf {111}}}$ values are estimated as a function of B content. $lambda _{{mathbf {100}}}$ of Fe–B film shows a positive value and increases with increasing the B content from 0 to 13 at. %, while the value of $lambda _{{mathbf {111}}}$ changes from negative to positive with increasing the B concentration. The B content dependence of $lambda _{s}$ for poly-crystalline Fe–B samples is explained by co- sidering the B content dependence of $lambda _{{mathbf {100}}}$ and $lambda _{{mathbf {111}}}$ determined with single-crystal film samples.

Description: Here, we report strain-induced high coercivity in La 0.7 Sr 0.3 CoO 3 (LSCO) films, which suffer in-plane tensile strains due to the positive lattice mismatch between the substrate and the LSCO bulk. The films on (011)-0.7Pb(Mg 1/3 Nb 2/3 )O 3 -0.3PbTiO 3 exhibit large uniaxial anisotropy, large coercivity, and high saturation magnetization at low temperature in contrast to the well soft magnetic behaviors in LSCO bulk. It is found that the coercivity of the 40 nm (001)-LSCO/SrTiO 3 film can be as high as 1.45 T at 10 K and the observed coercivity decreases rapidly as the thickness increases, though the Curie temperature is below room temperature. The large coercivity and anisotropy should be closely related to the strain-induced structural changes and the different orbital ordering of Co 3+ and Co 4+ ions. Meanwhile, the enhanced domain wall pinning by the tensile strain may also contribute to the observed high coercivity.

Description: The influence of the deviation of the easy axis $beta $ on the magnetic reversal of a hard/soft multilayer is investigated within a rigorous micromagnetic method when the thickness of the hard layer $t^{h^{vphantom {b}}}$ is finite. It is found that the pinning fields exhibit an angular symmetry where the minimum occurs at $beta =45 {^{circ }}$ , similar to that according to the well-known Stoner–Wohlfarth model. For intermediate soft layer thickness, the Kondorsly-like pinning is observed, where the pinning fields increase monotonically with $beta $ . On the other hand, the pinning field $H_{P}$ goes up monotonically with $t^{h }$ for all values of $beta $ when the hard layer thickness is less than roughly three times of its domain wall width.

Description: NdFeB bulk magnets were synthesized by spark plasma sintering (SPS) using the precursors of melt spun nanocrystalline Nd 10.15 Pr 1.86 Fe 80.41 Al 1.67 B 5.91 ribbons mixed with Zn and/or Dy 2 O 3 powders. The addition of 0.6 wt.% Zn or 2 wt.% Dy 2 O 3 is effective in improving the magnetic properties of the magnets, and their coercivities are about 11% or 15%, respectively, higher than that of the additive free magnet. Both additives can suppress the grain growth of Nd 2 Fe 14 B phase. Dy 2 O 3 is not beneficial to the densification during SPS, but Dy is considered to partly diffuse into the grains near particle boundaries and to form (Nd, Dy) 2 Fe 14 B phase. NdZn and NdZn 5 phases were observed in the SPSed magnets with Zn additions more than 1 wt.%, which leads to coarse grains and porosities between the particles. The magnet with combined additions of 2 wt.% Dy 2 O 3 and 0.6 wt.% Zn showed good thermal stability with small temperature coefficients and optimal magnetic properties with high coercivity and maximum energy product.

Description: The electrical resistance is one of the important properties for Nd 2 Fe 14 B magnets with low eddy-current loss. We have coated Nd–Fe–B melt-spun particles with CaF 2 by the liquid-phase coating technique and then performed hot-pressing and hot-deformation to make Nd 2 Fe 14 B/CaF 2 composite magnets. The morphology and distribution of CaF 2 in the magnets and its influence on the coercivity mechanism and the electrical properties of the Nd 2 Fe 14 B/CaF 2 magnets have been investigated by scanning electron microscope, hysteresisgraph, and four-probe resistivity meter. The morphology of CaF 2 depended on the liquid-phase synthesis parameters, especially the concentrations of the reactants. On the surface of Nd–Fe–B particles, there formed only a few CaF 2 nanoparticles and nanoflakes when 0.5 and 1 mol/l reactant aqueous solutions were used as precursors. With the increase of the concentrations of the reactants, there obtained a flake-shaped thin CaF 2 coating on the Nd–Fe–B particles. In addition, the CaF 2 coating became thicker, $sim 150$ –200 nm, with further increasing the concentrations of the reactants to 2 mol/l. After compaction and hot-deformation, the electrical resistances of the Nd 2 Fe 14 B/CaF 2 magnets fabricated using the concentrations of the reactants of 2 mol/l reached approximately 580 $mu Omega $ cm, which increased about 348% comparing with the corresponding pure Nd–Fe–B magnet. It is interesting to find that the coercivity of the Nd 2 Fe 14 B/CaF 2 composite magnets increased from 12.42 to 13.5 kOe when the concentrations of the reactants i- creased from 0.5 to 1.5 mol/l and then decreased to 10.2 kOe with further increasing the concentrations of the reactants to 2 mol/l. The reason for the increment of coercivity may be that CaF 2 nanoparticles and nanoflakes acted like lubricants that were beneficial to the rotation and the orientation of Nd 2 Fe 14 B particles during the hot-deformation process.

Description: As-cast Nd–Fe–B strips without an annealing treatment were treated by an appropriate hydrogenation–disproportionation–desorption–recombination (HDDR) process, and highly textured HDDR strip powders with uniform Nd-rich grain boundary layers can be obtained. The HDDR powders with a particle size of $50~mu text{m}$ show a Br of 1.13 T and a $_{i}H_{c}$ of 10.5 kOe. The crystal texture in the HDDR powders may come from the memory for the own crystallographic orientation and the casting texture of Nd 2 Fe 14 B columnar grains in the as-cast strips. The highly textured HDDR powders with uniform Nd-rich grain boundary layers can be used to prepare the fine-grained sintered magnets by a conventional jet-milling technique and sintering process.

Description: Magnetic properties and structure of sputter-prepared FePd thin films on the glass substrates by underlayering with refractory elements M (M = Nb, Mo, and W) have been studied. The structural analysis shows that FePd films have a (111) preferred orientation. All studied FePd films exhibit in-plane magnetic anisotropy. For single-layer FePd films, the coercivity ( $H_{c})$ and magnetic energy product [(BH) $_{mathrm {max}}]$ are increased with annealing temperature ( $T_{a})$ and reached the maximum value of 1.3 kOe and 3.8 MGOe in the sample annealing at 600 °C. With the further increase of $T_{a}$ , magnetic properties drop rapidly. Dependence of magnetic hardening on $T_{a}$ can be explained by dominant solid reactions in different region of $T_{a}$ including ordering and grain growth. Interestingly, magnetic properties of L1 0 -FePd are largely improved by underlayering with 5 nm-thick Nb, Mo, and W layers. Both the coercivity and energy product are significantly increased to 1.6 kOe and 4.9 MGOe for M = Nb, 2.5 kOe and 6.4 MGOe for M = Mo, and 3.3 kOe and 8.7 MGOe for M = W, respectively. Structural analysis suggests that this magnetic enhancement is related to both higher ordering degree and refined microstructure.

Description: The effect of wheel speed as well as an additive Cr 3 C 2 on the structure, crystalline texture, and magnetic properties of SmCo-based nanocrystalline magnets has been investigated. A low wheel speed of melt spinning of SmCo 6.8 (Cr 3 C 2 ) 0.2 promotes the formation of the Cr- and C-contained SmCo 7 main phase with a $langle 0001rangle $ out-of-plane texture, an average grain size of 38–60 nm, and a smooth ${M}$ – ${H}$ loop with sound rectangularity. On the other hand, for SmCo 4.8 (Cr 3 C 2 ) 0.2 alloys, ${H} _{mathrm{ci}}$ significantly enhances from 28.1 to 36.6 kOe and ${M} _{r}$ increases from 23.2 to 28.0 emu/g with an increasing wheel speed from 30 to 50 m/s. A high wheel speed of 50 m/s in SmCo 4.8 (Cr 3 C 2 ) 0.2 contributes to the formation of dendrite SmCo 5 grains with the short axis of about 20–50 nm and the long axis ranging from 100 nanometers to about 1 micrometer. An obviously preferential orientation along the $langle 0001rangle $ direction in SmCo 5 grains is observed, which could be confirmed by the transmission electron microscope analysis and anisotropic magnetic behavior. The addition of Cr 3 C 2 gives a hint toward the direction of texturing in SmCo-based magnets melt spun at high wheel speeds.

Description: In this paper, the structure and magnetic properties of the (Ce, Nd)–Fe–B magnets without Dy and Tb substitution have been investigated. The purpose of the investigation is to develop the applicable Ce–Fe–B magnets with Ce content over 50 wt.%. Sintered (Ce, Nd)–Fe–B magnets with the nominal composition of (Nd 1− x Ce x ) 30 (Fe, TM) bal B 1 ( $x=0$ –0.75) in wt.% were fabricated by advanced powder metallurgy processes. The effects of Ce substitution on the microstructure and magnetic properties of the (Ce, Nd)–Fe–B magnets were discussed. It was found that the (Ce, Nd)-rich boundary phase with lower melting point is helpful to obtain improved boundary microstructures and refined grain magnets. Good magnetic properties of Br = 13.5 kG, $H_{mathrm {cj}}= 9.5$ kOe, and $(BH)_{mathrm {max}} = 42.8$ MGOe were obtained in the Dy-free (Ce, Nd)–Fe–B magnets with 30 wt.% Ce substitution. A higher coercivity (>10 kOe) has been achieved in the Ce–Fe–B type magnets by the modifications of alloy compositions and the optimization of preparation conditions, in which the proportion of Nd and/or Pr is lower than 35 wt.% of the total rare-earth content.

Description: The effect of Dy addition on the magnetic and mechanical properties of sintered Nd-Fe–B magnets prepared by the double-alloy powder mixed method was investigated. The results showed that the intrinsic coercivity of sintered Nd-Fe–B magnets increases gradually, and the squareness factor of sintered Nd-Fe–B magnets declines with increasing Dy content. The Vickers hardness of sintered Nd-Fe–B magnets increases with increasing Dy content, and the maximum fracture toughness of sintered Nd-Fe–B magnets is obtained when the Dy content is 2 wt%. The bending strength of sintered Nd-Fe–B magnets first declines, and then increases with increasing Dy content. The minimum bending strength of sintered Nd-Fe–B magnets is obtained at the Dy content of 2 wt%. The microstructure showed that the distribution of Dy content in main phase was not uniform because of the Dy diffusion of double-alloy mixed powder during the sintering process.

Description: A series of Ce x Fe bal B 6 ( $x=12$ , 14, 17, 19, and 23 wt%) ternary ribbons was prepared by melt-spinning. Magnetic properties and the microstructure of the Ce–Fe–B ribbons with different Ce contents were investigated. The X-ray diffraction results indicated that multiphase coexisted in the as-spun Ce–Fe–B ribbons, which contained Ce 2 Fe 17 , CeFe 2 , Ce-rich phase, Fe-rich phase, cerium oxide, and iron oxide. The magnetic properties, microstructure, and phase composition of the ribbons were directly affected by the cerium content. The magnetic properties could be obtained by exchange coupling between the hard and soft magnetic phases in the pure ternary Ce–Fe–B ribbons. Furthermore, by heat treatment, the magnetic properties of the as-spun Ce–Fe–B ribbons could be optimized. The highest magnetic properties of $H_{{mathrm{cj}}}=6.2$ kOe, $B_{mathrm{ r}}=6.9$ kGs, and $(BH)_{mathrm{ m}}=8.6$ MGOe were obtained in Ce 17 Fe bal B 6 magnets.

Description: To obtain the excellent magnetic properties for the Ce substitution magnets, we proposed a dual-main-phase method to prepare the high-permanence (CePrNd)–Fe–B magnet with low cost. The main phase in this method means the hard magnetic phase with high anisotropy field. Compared with the traditional sintered method adjusting the composition of the magnet, the dual-main-phase method can also design the distribution of the main phase in the magnet, which makes the structure satisfy the demand of the magnet with outstanding properties. Compared with the magnet prepared by the single-alloy method, the coercivity of the magnet prepared by the dual-main-phase method is dramatically enhanced from 7.7 to 12.1 kOe, which may be due to the distribution of the grain boundary phase between the different kinds of main phases.

Description: The waste sintered Nd–Fe–B magnets were recycled to fabricate anisotropic bonded magnets by the combination of hydrogen decrepitation (HD) and NdH x nanoparticle modification. Magnetic properties of the recycled magnetic powders and bonded magnets were investigated. Adding NdH x nanoparticles to HD powders may increase the coercivity of the recycled powders. The HD powders with 10 wt. % NdH x degassed at 973 K for 5 h bear magnetic properties of $B_{r}$ of 9.36 kGs and $H_{mathrm{ ci}}$ of 12.36 kOe. The recycled bonded magnet exhibits good magnetic properties of $B_{r}= 7.61$ kGs, $H_{mathrm{ ci}}= 12.93$ kOe, and $(BH)_{{textrm {max}}}= 11.56$ MGOe.

Description: Ultrafine-grained sintered Nd–Fe–B magnets were produced from jet-milled hydrogenation–disproportionation–desorption–recombination powders in a proper sintering condition. The coercivity of $sim 15$ kOe was obtained by sintering below 950 °C, and the average grain size was $〈1~mu text{m}$ . For the newly fine-grained magnets, a higher magnetic field is needed to magnetize them, giving rise to a two-step initial magnetization curve involving domain wall pinning at the grain boundary phase. Microstructure observation indicated that the Nd-rich phases did not encapsulate the 2:14:1 phases effectively, resulting in defects and interactions between adjacent 2:14:1 grains, which are responsible for the relatively low coercivity of the fine-grained magnets.

Description: The microstructure and magnetic domain-wall motion of a sintered Sm(Co,Fe,Cu,Zr) z permanent magnet with different Cu and Fe contents was investigated by Lorentz transmission electron microscopy. The domain-wall motion under different magnetic fields indicates that most domain walls are strongly attracted by the SmCo 5 boundary phases, but some of them are repulsed to the Sm 2 Co 17 cell phase. Differences in Cu and Fe distribution at the SmCo 5 cell boundary phase and the SmCo5/Sm 2 Co 17 interface are considered to result in domain-wall behavior, and a larger Cu and a smaller Fe content in the sample make the attractive pinning force stronger and, therefore, coercivity is higher.

Description: Motors of hybrid vehicles and electric vehicles are anticipated to become smaller and have higher rotational speed. However, the small motors with high rotational speed may demagnetize the permanent magnets of motors by applying a high-frequency field of $sim 10$ kHz at temperatures over 400 K. This demagnetization also depends on a static dc-field $sim 3$ –4 kOe. We call this demagnetization phenomena magnetic fatigue. In this paper, magnet behaviors within a high-frequency field and at high temperature were simulated using a micromagnetic simulator.

Description: Although increase in thickness of a Nd–Fe–B film magnet is indispensable to provide a sufficient magnetic field, it was difficult to suppress the peeling phenomenon due to the different values of a linear expansion coefficient for a Si substrate and a Nd–Fe–B film even if a buffer layer such as a Ta film was used. In this report, it was confirmed that a control of the microstructure for pulsed laser deposition-fabricated Nd–Fe–B films enabled us to increase the thickness up to approximately 160 $mu$ m without a buffer layer on a Si substrate. Namely, we found that the precipitation of the Nd element at the boundary of Nd–Fe–B grains together with the triple junctions due to the composition adjustment is effective in suppressing the destruction of the samples through an annealing process. The magnetic properties of the prepared films were comparable with those of previously reported ones deposited on metal substrates. Although the mechanism is under investigation, the above-mentioned film had stronger adhesive force compared with that of a sputtering-made film. Resultantly, no deterioration of mechanical together with magnetic properties could be observed after a dicing process.

Description: The temperature dependence of magnetic anisotropy in the low-temperature phase MnBi thin films is discussed in conjunctionwith saturation magnetization and lattice constants. It is experimentally found that $K_{u}$ is inversely proportional to the eighth power of the saturation magnetization $M_{s}$ . It is also found that the $K_{u}$ is proportional to the unit-cell volume. The calculation based on first principles of magnetic anisotropy energy as a function of lattice constants ( $a$ and $c$ ) and statistical simulations of its spin-temperature dependence is consistent with the experimental results. However, the spin-reorientation transition taking place at 100 K is not accounted for by the present calculation.

Description: (La 0.35 Ce 0.65 ) 2 Fe 14– x Si x B ( $x=0.0$ , 0.5, 1.0, 1.5, 2.0) ribbons were prepared by the melt-spinning technique, and La–Ce mischmetal with impurities was used as the starting material. The effects of Si substitution on phase formation and room temperature magnetic properties were investigated by X-ray diffraction and a vibrating sample magnetometer. It was found that the optimal wheel velocity dropped dramatically when a small amount of Si was introduced. It dropped from 20 to 15 m/s while Si concentration increased from $x=0.0$ to 0.5. We also found that increasing the Si content can damage the phase formation of the 2:14:1 structure, which is different from the case in Nd 2 Fe 14 B and even in Ce 2 Fe 14 B. The substitution of Si for Fe does not enhance the coercivity of (La 0.35 Ce 0.65 ) 2 Fe 14 B magnets effectively. The result indicates that the early findings about the element substitution and addition in Nd 2 Fe 14 B cannot be simply copied in research studies of (La 0.35 Ce 0.65 ) 2 Fe 14 B.

Description: Nanocomposite Nd 2 Fe 14 B/SmCo 5 permanent magnets with different weight ratios have been prepared by spark plasma sintering mixtures of homemade amorphous SmCo 5 powders and commercially available Nd 2 Fe 14 B powders. The magnetic properties of the nanocomposite magnets are sensitive to the ratio of the two hard phases. The peak (BH) max value of 14.4 MGOe is obtained at the SmCo 5 /Nd 2 Fe 14 B ratio of 4:1, which is $sim 50$ % higher than that of the single-phase SmCo 5 magnet prepared under the same preparation conditions. Hysteresis loop of the nanocomposite magnet shows the characteristics of single-phase magnet due to strong exchange coupling between the two phase grains. At high temperatures, the nanocomposite magnets exhibit greatly improved thermal stability compared with the single-phase Nd 2 Fe 14 B magnet.

Description: The interstitial rare earth–iron compounds exhibiting a variety of magnetocrystalline anisotropies, large saturation magnetization, and high Curie temperature provide the basis for high-performance magnetic materials. In this paper, a manufacturing process for mass production of anisotropic magnetic powders has been successfully developed for Nd(Fe, M) 12 N (NdFeN) and Sm 2 Fe 17 N 3 (SmFeN) compounds with uniaxial anisotropy. The magnetic powders of Nd(Fe, M) 12 N have maximum energy products [(BH) max ] around 22 MGOe. The calendar magnets of NdFeN show the rolling anisotropy and have a (BH) max up to 5.9 MGOe with excellent mechanical properties and good anticorrosion ability. The (BH) max of SmFeN magnetic powders is up to 41 MGOe, which is favorable for fabricating high-performance injection magnets and extrusion magnets. On the other hand, it was found that cone or planar anisotropic R 2 Fe 17 N x (R = Ce, Pr, Nd) and paraffin composites can improve the Snoek limit and exhibit a high microwave reflection loss of up to −35 dB at about 14 GHz, presenting an advantage for application as a high-performance thin-layer microwave absorber. These results open up broad prospects for technological applications using interstitial modified compounds.

Description: Anisotropic Nd–Fe–B films with high performance have been prepared by dc magnetron sputtering on heated Si(100) substrates. The influences of sputtering power, target composition, deposition temperature, and annealing condition on the magnetic properties of Nd–Fe–B films were investigated systematically. The X-ray diffraction patterns showed that the Nd–Fe–B grains are aligned with their c-axes pointing normal to the film plane. It was found that the magnetic properties are sensitive to the target composition, deposition temperature, and sputtering power. The maximum energy product achieved (378 kJ/m 3 ) is comparable with that of high-quality Nd–Fe–B sintered magnets.

Description: To improve the interface magnetism of Co x Fe 3– x O 4 (CFO) films that are grown on MgO substrates and exhibit extremely large perpendicular magnetic anisotropy, we attempted to insert two different spinel-type oxides [CoCr 2 O 4 (CCO) and MgTi 2 O 4 (MTO)] between the CFO films and their MgO(001) substrates. Although both buffer layers were epitaxially grown on MgO(001), the CFO films grown on CCO/MgO(001) became polycrystalline with a significantly lower level of magnetization, while the magnetization of the CFO films on MTO/MgO(001) fell as a function of the thickness of the MTO layer. A secondary ion mass spectroscopy analysis revealed a remarkable interdiffusion of Co and Mg.

Description: To study the influence of soft magnetic phase coating on magnetic properties of hard/soft phase nanocomposite materials, the coating of soft magnetic FeCo on hard magnetic SmCo 5 nanochips was performed via a sonochemical process. First, anisotropic hard magnetic SmCo 5 nanochips were prepared by surfactant-assisted high-energy ball milling in the presence of oleic acid as a surfactant and heptane as a solvent. Then, the soft magnetic FeCo was coated on SmCo 5 nanochips by the reduction of FeCl 3 and CoCl 2 with hydrazine using ultrasonic waves in the presence of NaOH. The amount of the soft phase coating on the hard magnetic nanochips was controlled by varying the initial ratio of soft-phase precursors to hard magnetic particles during the reaction. The soft-phase coating on the hard phase chips has lead to an enhanced remanence due to an exchange coupling between the soft and the hard magnetic phases at optimal hard/soft phase ratios. The composite chips also show a strong magnetic anisotropy when aligned in a magnetic field. The anisotropic SmCo 5 /FeCo core/shell nanocomposite chips are promising candidates as building blocks for high-performance anisotropic nanocomposite bonded or fully dense magnets via a bottom-up fabrication approach.

Description: We have investigated the effect of nonmagnetic cap layers for Nd–Fe–B thin films with a small addition of rare-earth element. Remarkable enhancement of the coercivity was obtained for the Nd–Fe–B thin film on the epitaxially grown Mo buffer layer deposited at 500 °C followed by the postannealing at 550 °C. Especially, the highest room temperature (RT) coercivity $H_{C}$ of 31.5 kOe can be obtained for the Nd–Fe–B (16 nm)/Nd-Cu (0.75 nm)/Al (0.6 nm) thin film. This result suggests that a eutectic reaction among Nd, Cu, and Al elements was occurred during the postannealing, and then the grain boundary between Nd 2 Fe 14 B main phases is refined by the diffusion of the cap layer. We demonstrated that the Nd–Fe–B thin film showed large $H_{C}$ exceeding 30 kOe at RT without using heavy rare-earth elements.

Description: An observation of microstructure revealed that a laser-irradiated Nd–Fe–B target under the laser energy density above 10 J/cm 2 enabled us to prepare isotropic nano-composite thick-film magnets with good magnetic properties due to a dispersed $alpha $ -Fe + Nd–Fe–B structure. The formation of the structure is attributed to the etching process of a target during a deposition. Moreover, the control of composition in the nano-composite film enhanced the ( $BH$ ) $_{mathrm { {max}}}$ value up to $sim 130$ kJ/ $text{m}^{mathrm { {3}}}$ .

Description: The magnetism of Cr 2 O 3 thin films on $alpha $ -Al 2 O 3 is investigated using first-principle calculations by considering three Cr 2 O 3 films having thicknesses of 4.1 Å (I), 6.7 Å (II), and 10.9 Å (III) and comparing the spin structures of free films with those on the substrate. For the free films, we find that I is ferromagnetic (FM), while II and III are antiferromagnetic (AFM). On the substrate, the Cr 2 O 3 film I is also FM. Films II and III remain basically AFM, although the spins of the top Cr layers change sign in both films, creating a ferrimagnet with a small uncompensated net moment.

Description: Nanoparticles of cobalt oxide (Co 3 O 4 ), of size 4.2 nm, were fabricated by heating Cobalt (Co) nanoparticles synthesized using dimethyl sulfoxide solvent. The temperature dependence of magnetization for field cool and zero field cool processes of Co 3 O 4 nanoparticles shows the bifurcation at 44 K. A cusp is observed at 1 T and higher applied fields indicating antiferromagnetic behavior in the system with the Néel temperature ( $T_{N}) sim 34$ K. The estimated magnetic entropy change ( ${-mathrm {Delta }S}_{M}$ ) for the Co 3 O 4 nanoparticles suggests the unusual behavior in magnetic phase transformation of the Co 3 O 4 nanoparticles. A normal magnetocaloric effect (MCE) at $T sim 44$ K and inverse MCE at $T sim 34$ K are observed. These results correlate the magnetocaloric properties to the magnetic phase transitions in the Co 3 O 4 nanoparticle system.

Description: MnZn ferrite nanoparticles (NPs) with Mn x Zn 1– x Fe 2 O 4 ( $x=0$ and 0.6) compositions have been synthesized by sol–gel process. As prepared (AP) particles were annealed at 1200 °C in air to compare the physical properties of NPs with their bulk counterparts. The crystallite sizes of AP samples were estimated to be 18 nm for $x=0$ and 11 nm for $x=0.6$ . The cationic disorder was evaluated from the Rietveld analysis of X-ray diffraction (XRD) data, which decreases with increasing annealing temperature. The average particle size of the AP samples is observed to be below 20 nm and transform into single-phase spinel structure of $sim 500$ nm long cylindrical rods of 60 nm-diameter for $x=0.6$ , when annealed at 1200 °C in air. The magnetic properties of AP NPs show ferrimagnetic behavior below the blocking temperature ( $T_{B})$ and superparamagnetic behavior above the $T_{B}$ . The observed magnetic characteristics corroborate well with the structural parameters obtained from the Rietveld analysis of the XRD data.

Description: This paper describes the magnetization dynamics of Ni–Fe dot array estimated by the ferromagnetic measurement with the coplanar waveguide. The magnetic configuration of the dot changes from a multi-domain to a closure domain as the dot size decreases. The switching field at which a single domain is formed increases with the dot size reduction, which may be attributed to the enhanced magnetostatic energy. On the other hand, the damping constant decreases monotonically from 0.029 to 0.012 for the major axis length $〈 1~mu text{m}$ , and their values are higher than that of the Ni–Fe film ( $alpha =0.009$ ). The reason for these differences is that the demagnetization field distribution near the dot edge becomes inhomogeneous with the dot size reduction. On the basis of these results, it is revealed that the extrinsic factor, such as the inhomogeneous demagnetization field distribution, strongly influences on the damping constant. These results also suggest that the correlation with the magnetic configuration of the dot is one of the most important to understand the magnetization dynamics in submicrometer-sized magnets in detail.

Description: An RF 3 (R = La, Ce, Pr, Nd, and Dy)-doped Nd 13.6 Fe 73.6 Co 6.6 Ga 0.6 B 5.6 hot-pressed magnet was prepared using melt-spun flakes. The substitution of Nd in Nd–Fe–B flakes by rare-earth dopant in the hot-pressed magnets doped with various RF 3 and its effect on coercivity were investigated. In the RF 3 -doped Nd 13.6 Fe 73.6 Co 6.6 Ga 0.6 B 5.6 magnet hot pressed at the modest temperature (735 °C), the dopants Ce, Pr, Nd, and Dy actively substituted Nd in the region near the flake surface to form the thin shell in the flake. RF 3 (R = Dy, Nd, and Pr) doping achieved significant coercivity enhancement in the hot-pressed magnet, and it was attributed to the enhanced anisotropy field of the Nd 2 Fe 14 B-type grains (for Dy and Pr doping) and grain boundary restructuring (for Nd doping) in the shell. The most profound coercivity enhancement as high as 5 kOe was achieved in the DyF 3 -doped magnet. Doping with the light rare-earth elements using RF 3 (R = La and Ce) led to poor coercivity enhancement with respect to the RF 3 (R = Dy, Nd, and Pr) doping.

Description: In this paper, we have deposited continuous and uniform Ni–B nanotubes with a length of 20 $mu $ m and outer diameter of 400 nm via an electroless deposition method and investigated their magnetic properties. We show that as the pH of the electroless deposition bath increases, the B content of the Ni–B deposit decreases. As the boron content decreases the specific saturation magnetization ${sigma _s}$ increases, with a maximum value of 33.7 J T −1 kg −1 obtained for a composition of Ni 88 B 12 . We have found that the magnetization of the Ni–B nanotubes increases after annealing due to crystallization of amorphous Ni–B, while the nanotube structure is still preserved at high temperatures. A maximum specific saturation magnetization of 46.3 J T −1 kg −1 was measured after annealing at 500 °C for 1 h. Our results are analyzed in comparison to bulk Ni metal with specific saturation magnetization of 55.4 J T −1 kg −1 . The electrolessly deposited nanotubes are shown to have a vortex mode reversal mechanism, which is attributed to the wall thickness in comparison to the outer diameter of the nanotubes.

Description: In conventional recording theory, the transition width should be minimized by writing the transition at the location of the maximum head-field gradient, and this should be achieved by setting the coercivity equal to the head field at the location of the maximum head-field gradient (taking appropriate account of the variation of coercivity with field angle). A natural assumption in bit-patterned media is that the system could be optimized by setting the island switching field in a similar manner. In this paper, we investigate what strategy of optimization gives the minimum error rate or the maximum write-window.

Description: We report on the microstructure, phase constitution, mechanical properties, and magnetocaloric effect (MCE) of Cu-bonded La(Fe,Si) 13 composites prepared by hot pressing (HP) at different temperatures. It was found that the final density of composites greatly relies on the initial powder size and pressing temperature. Finer powders lower the temperature needed for fully compacting. HP at 700 °C suits finer La(Fe,Si) 13 powders to approach the theoretical density and high mechanical strength, and 800 °C for coarse powders. At the same time, the drastic diffusion reaction takes place at evaluated temperature due to Cu–La eutectic point. Combined with the influence of press-induced grain breaking, the MCE was decreased with respect to the pure La(Fe,Si) 13 phase.

Description: Control of the magnetic anisotropy under different strain states is important for the manipulation of magnetization in flexible spintronic devices. Here, the electric field control of magnetic anisotropy was investigated in flexible Fe 81 Ga 19 (FeGa)/polyvinylidene fluoride multiferroic heterostructures under different compressive strains. The initial uniaxial magnetic anisotropy is enhanced with increasing the compressive strain. When the strain is larger than 0.06%, the electric field can only change the strength of the magnetic anisotropy but cannot change its direction. When the strain is smaller than 0.06%, the electric field of 267 kV/cm can reorientate the easy axis by 90°. The present results may be helpful for designing flexible multiferroic devices with a suitable initial strain in order to realize the 90° reorientation of the magnetization.

Description: In this paper, we present a detailed study on the critical property around the ferromagnetic (FM)–paramagnetic phase transition of Pr 0.6 Sr 0.4 MnO 3 nanoparticles (NPs) with different crystallite sizes ( $d = 39$ –88 nm), which were synthesized by the combination of the solid-state reaction and mechanical milling methods. The magnetic results show that the samples undergo the second-order phase transition. The values of the Curie temperature ( $T_{C}$ ) slightly decrease from 291 to 286 K while the saturation magnetization ( $M_{S}$ ) decreases from 89.7 to 76.3 emu/g and the coercivity ( $H_{C}$ ) increases from 322 to 585 Oe with decreasing $d$ from 88 to 39 nm, respectively. Based on the modified Arrott plot method and the isothermal magnetization data around $T_{C}$ , we have determined the values of critical exponents ( $beta , gamma $ , and $delta $ ) and $T_{C}$ for the samples. The critical exponents $beta = 0.486$ – 0.495, $gamma = 1.009$ – 1.042, and $delta = 3.038$ – 3.118 obtained are close to those expected for the mean field theory ( $beta = 0.5, gamma =1$ , and $delta = 3$ ). This proves that long-range FM interactions are present in the NPs. Furthermore, $beta $ values are smaller than 0.5, indicating the existence of magnetic inhomogeneity in the NPs. Besides the investigation into the critical behavior, the magnetocaloric effect of the NPs is also investigated.

Description: It is necessary to find alternative regenerator materials for lead because lead is toxic and prohibited in any device by Restriction of Hazardous Substances (RoHS). In this paper, the low temperature heat capacities and mechanical properties of the multiphase Er 3+ x Ni alloys are studied. The results show that Er 3+ x Ni alloys consist of Er and Er 3 Ni phases. The specific heat capacities of Er 10.819 Ni and Er 4.436 Ni are higher than lead from 5 to 90 K. The addition of Er makes Er 3+ x Ni alloys have much more excellent mechanical properties than pure Er 3 Ni. The compressive strength of Er 4.436 Ni, Er 6.351 Ni, and Er 10.819 Ni alloys as measured are all more than six times larger than Er 3 Ni. And there is a convert from brittle fracture to ductile fracture along with the increase in the content of Er. The study of mechanism of fracture of Er 3+ x Ni alloys reveals that the fractures of the alloys are cleavage fracture and quasi-cleavage fracture.

Description: In this paper, we investigated the influence of particle size and filling factor of flake-type Galfenol powders on sensing performance of Galfenol composite-based magnetostrictive patch transducers. A small demagnetizing field is generally expected for flake-type powders along the in-plane of particles, resulting in enhancing low field sensitivity of the composite patch with well aligned particles. The composite patch composed of the Galfenol flakes and epoxy resin was fabricated with a specially designed uniaxial comb shape to promote magnetic shape anisotropy effect of the patch itself and to enhance directional sensitivity of the patch for guided lamb wave (GLW) applications. The influence of particle size and filling factor of the Galfenol composite patch was evaluated based on the direct A0 mode (the fundamental flexural mode) in received GLW signal data. The linear increase in sensing performance was distinctly observed in the composite patches as the filling factor of Galfenol flakes increased. In addition, the Galfenol composite patches exhibited an improved sensitivity by increasing the size of the Galfenol particles.

Description: The structural, magnetic, and martensitic transition properties of Ni 45− x Co 5 Mn 40+ x Sn 10 ( $x=2$ , 4, 6, and 8) alloys are investigated systematically. X-ray diffraction reveals that the alloys mainly exhibit a tetragonal phase at room temperature, but also a small amount of impurity phase when the Mn content is >46%. The temperature dependence of magnetization indicates that there are two different magnetic transitions in the alloys, the Curie transition and the martensitic transition. With the substitution of Mn for Ni, the Curie temperature of alloys remains almost unchanged, while the martensitic transition temperature decreases, which is attributed to the decrease in the valence electrons concentration. In particular, the strong coupling between magnetism and structure occurs in Ni 45− x Co 5 Mn 40+ x Sn 10 alloys, and the Ni 43 Co 5 Mn 42 Sn 10 alloy exhibits a large magnetic entropy change of 30.6 Jkg $^{-1}text{K}^{-1}$ at a field change of 3 T in martensitic transition, making it a good candidate for magnetic refrigeration materials.

Description: In this paper, we report the giant electric-field (E-field)-induced magnetic anisotropy and magnetization switching in CoNi/Pb(Mg 1/3 Nb 2/3 )O 3– x PbTiO 3 (PMN-PT) magnetoelectric heterostructures. For CoNi/PMN-30%PT, the E-field-induced anisotropy shows a volatile behavior; whereas for CoNi/PMN-32%PT, a large and nonvolatile E-field-induced anisotropy field up to 54 kA/m is observed. These behaviors can be understood by measuring the strain versus the E-field curves of two kinds of substrates. On the basis of the E-field-induced nonvolatile magnetic switching, two stable magnetization states defined by applying E-field pulses were demonstrated in CoNi/PMN-32%PT heterostructure, which paves a new way for voltage-write magnetic random memory devices.