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.