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  • 1
    Electronic Resource
    Electronic Resource
    Effects of grain size dispersion on noise in longitudinal thin film media : 37th Annual conference on magnetism and magnetic materials (1993)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 73 (1993), S. 5548-5550 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The effect of grain size dispersion on medium noise in longitudinal thin film recording media is studied by micromagnetic modeling. A previous micromagnetic model has been extended for modeling films with grain size variation. It is found that for the typical thin film media, moderate grain size dispersion in the film does not affect the media noise at low recording densities. At high recording densities, when adjacent transition boundaries percolate, the film with grain size dispersion exhibits a less degree of superlinear noise enhancement than the film with identical size grains. It is concluded that for films with medium noise dominated by magnetic interactions, moderate grain size dispersion slightly suppresses the collective magnetization processes at high recording densities, thereby, reducing medium noise.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.353646
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  • 2
    Electronic Resource
    Electronic Resource
    Method for investigating the reversal properties of isolated barium ferrite fine particles utilizing magnetic force microscopy (MFM) : 37th Annual conference on magnetism and magnetic materials (1993)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 73 (1993), S. 6716-6718 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The reversal properties of isolated barium ferrite recording particles with Co-Ti substitution (BaFe12−2xCoxTixO19) are studied by a newly developed magnetic force microscopy (MFM)-based technique. The size dependence of the switching field on particles with diameters ranging from 30 to 80 nm were investigated. A decrease in the switching field was observed, which corresponds to a decrease in the particle diameter below 50 nm. This indicates thermally assisted switching in small size particles. As the diameter increases, the switching field reaches a maximum at 55 nm then sharply decreases. An atomic force microscopy (AFM) profile of the particle's thickness shows that the aspect ratio variation among these particles cannot account for the observed difference in the switching field. Thus, it is concluded that incoherent reversal is occurring in particles with diameter greater than 60 nm.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.352512
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  • 3
    Electronic Resource
    Electronic Resource
    Micromagnetic study of dynamic domain instability in magnetoresistive sensors (abstract) : 37th Annual conference on magnetism and magnetic materials (1993)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 73 (1993), S. 6241-6241 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Dynamic domain instability in magnetoresistive sensors produces noise in the output voltage pulses and forces complex head designs to suppress the irregular domain activities. In this paper, the micromagnetic modeling study of dynamic domain instability is presented. A Permalloy magnetoresistive sensor 10 μm in width, 2.5 μm in height, and 200 A(ring) in thickness is modeled by a two dimensional array containing 512×128 cubic elements with identical intrinsic magnetic properties of Permalloy material. The Landau–Lifshitz equation is utilized for calculating the dynamic magnetic domain configurations as well as structures within domain walls. The study focuses on the transient processes that generate complex multidomain structures and the irregular dynamic domain activities. Figure 1 shows a simulated static "single'' domain configuration, obtained by initially aligning the magnetization along the long axis of the Permalloy stripe. Circular edge domains are formed with patterns well agree with experimental observations. A high frequency (200 MHz) sinusoidal external field (amplitude 40 Oe) is then applied vertically with 10° deviation. Figure 2 shows the transient domain configuration at the time t=0.6T (T=period). The center portion of the stripe have become multidomain with irregular domain configuration and 180° Neel walls containing irregularly distributed Bloch lines and crossties. Note the irregularity of the domain configuration even though the material is homogeneous. The magnetization within the Neel walls alternates its direction along the walls. Detailed analysis of the onset of the multidomain state will be presented. Investigation of dynamic domain behavior under various bias schemes will be reported.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.352710
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  • 4
    Electronic Resource
    Electronic Resource
    Self-organized behavior in thin-film recording media : 35th annual conference on magnetism and magnetic materials (1991)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 69 (1991), S. 4709-4711 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Magnetization domain structures in thin metallic films utilized as recording media are modeled by a cellular automation on a two-dimensional triangular lattice. This alternative approach permits significantly large arrays ((approximately-greater-than) 106 grains) to be investigated as compared to an exact calculation (≈ 5 × 103 grains). Thus a study of the statistical distribution of the domain sizes and their power spectra can be made. Magnetostatic interactions and intergranular exchange coupling are included in a simple manner so that collective behavior is incorporated. It is found that away from the saturation remanent state, the distribution of the size of the avalanches (or the number of sites reversed in a single reversal sequence) follows a power-law behavior: D(S) = AS−α where S is the avalanche size and α varies in the vicinity of 1 depending on the interaction strength. The reversal field keeps the system marginally stable. It is found that the reproduce noise power varies as the derivative of the M-H loop.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.348255
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  • 5
    Electronic Resource
    Electronic Resource
    Reversal mechanisms and domain structures in thin-film recording media (invited) : 35th annual conference on magnetism and magnetic materials (1991)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 69 (1991), S. 6084-6089 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Magnetization reversal in longitudinal and perpendicular thin films is studied via computer simulation. Collective micromagnetic processes and the formation of magnetization patterns driven by magnetostatic interactions and intergranular exchange coupling is analyzed. In longitudinal thin films, it is found that a reversal starts by formation of magnetization vortices. The collective formation of vortices yields elongated reverse regions along the direction of the applied field. Intergranular exchange coupling enhances these magnetization structures and results in large-size domains. Reversal of a typical perpendicular film (CoCr) consists of discrete nucleation processes. Each individual process is characterized by a planar chain nucleation mode. These collective micromagnetic processes cause film magnetic properties to be significantly different from those of a simple assembly of noninteracting grains. Medium noise in perpendicular films occurs mainly away from transitions in distinct contrast to longitudinal films in which the noise is concentrated at transition centers. Intergranular exchange coupling increases the medium noise in all films.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.347776
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  • 6
    Electronic Resource
    Electronic Resource
    High speed characteristics of thin film write heads at deep submicron track width (2000)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 87 (2000), S. 5416-5418 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: This article presents a micromagnetic study of the dynamic magnetic switching process in the pole tip region of stitched-pole thin film write heads. The impacts of track width reduction and pole material saturation moment on the high frequency performance of the heads have been investigated. It is found that the magnetic switching process of the pole tip region at low recording frequencies can be characterized by three stages: the nucleation of a vortex (or vortices), followed by the motion of the vortex (or vortices), and finally the annihilation of the vortex (or vortices). At high frequencies, however, a residual vortex (or vortices) will always remain in the pole tips, resulting in lower head field amplitude. Frequency roll-off characteristics of the head field response have been calculated. The roll off is the result of residual vortex (or vortices), and the vortex moving speed limits the operational frequency range of the head. Reducing the track width lowers the head field 3 dB roll-off frequency. The simulation also finds that the use of 45/55 NiFe, which has significantly higher moment than permalloy, results in higher roll-off frequency as compared to permalloy. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.373361
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  • 7
    Electronic Resource
    Electronic Resource
    Ultrahigh density vertical magnetoresistive random access memory (invited) (2000)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 87 (2000), S. 6668-6673 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: In this paper, we present the vertical magnetoresistive random access memory (VMRAM) design based on micromagnetic simulation analysis. The design utilizes the vertical giant magnetoresistive effect of the magnetic multilayer. By making the memory element into a ring-shaped magnetic multilayer stack with orthogonal paired word lines, magnetic switching of the memory device becomes very robust. The design also adopts the readback scheme in pseudo spin valve MRAM so that only one transistor is needed for each bit line which can connect hundreds of memory elements, yielding a very high area density. It is estimated that the ultimate area density for the VMRAM is 400 Gbits/in.2. It is suggested that this memory design has the potential to not only replace the present semiconductor memory devices, such as FLASH, but also the potential to replace DRAM, SRAM, and even disk drives. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.372805
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  • 8
    Electronic Resource
    Electronic Resource
    Effect of grain size and crystalline orientation on magnetic switching (1999)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 85 (1999), S. 4776-4778 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The effect of crystalline orientation and grain size on the switching behavior for patterned face-centered-cubic Co film elements has been investigated through micromagnetic modeling. It is found that the switching field of the Co film element exhibits significant dependence on crystalline orientation and grain size. Large grain results in large switching field for polycrystalline Co film element. The switching fields of (001) and (110) oriented single crystal elements are much higher than that of the (111) oriented single crystal elements. It is also found that the effect of crystalline anisotropy on the switching behaviors strongly depends on the magnetization reversal mode. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.370478
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  • 9
    Electronic Resource
    Electronic Resource
    Investigation of advanced position error signal patterns in patterned media (2000)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 87 (2000), S. 5117-5119 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A potential approach to extending current thin film media to 100 Gbits/in2 recording density is physical patterning of the media, perhaps via an etching technique. An advantage of patterning is the capability of creating advanced position error signal (PES) patterns that are difficult or impossible to generate with writing by a recording head. This study uses spin stand tester to investigate various PES patterns generated by a focused ion beam etching technique on conventional thin film disks. For all practical purposes, the patterned PES eliminates transition noise, track edge noise, and erase band, therefore, demonstrates a much better PES signal than conventionally written servo patterns. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.373267
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  • 10
    Electronic Resource
    Electronic Resource
    Texture and surface/interface topological effects on the exchange and coercive fields of NiFe/NiO bilayers (1997)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 81 (1997), S. 340-343 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The texture and surface/interface topological effects on the exchange field Hex and coercivity Hc in rf-sputtered NiO/NiFe bilayers were studied. The NiO/NiFe bilayers with NiO crystalline textures of (111), (200), and (220), and different surface/interface roughness, were fabricated by changing the sputtering conditions. The Hex of the NiO/NiFe bilayers was inversely proportional to the thickness of NiFe. The NiO/NiFe bilayers with different NiO textures of (111) dominant, (200) dominant, or combinations of (111), (200), and (220), respectively, showed almost the same dependence of Hex on NiFe thickness. Thus, Hex was insensitive to the texture of NiO films. The surface/interface roughness has a significant effect on Hc of the NiO/NiFe bilayers. By controlling the sputtering process, NiO (45 nm)/NiFe (10 nm) bilayers with a Hex of 39 Oe, a Hc of 4.1 Oe, and an Hex/Hc ratio of 9.51 could be obtained. A new parameter of Hex/Hc was introduced to describe the exchange coupling and coercive properties in ferromagnet/antiferromagnet coupled bilayers. A large Hex/Hc ratio is very desirable for spin-valve structures. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.364116
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