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  • 1
    Electronic Resource
    Electronic Resource
    Thermal relaxation over a barrier in single domain ferromagnetic particles (1990)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 67 (1990), S. 4505-4507 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We present a summary of our general results on the theory of magnetization switching via thermal decay (the classical case) in a small, single domain ferromagnetic (superparamagnetic) particle. Our results allow us to calculate the prefactor of the thermal decay rate and apply them to realistic models, viz., to systems of cubic symmetry (both the Fe and Ni type) and to uniaxial systems with tetragonal, triclinic, and hexagonal symmetry in the basis plane. In each case an external magnetic field parallel to an easy axis can be present. We compare our results with the strictly axially symmetric model often quoted in the literature. This model is singular in that it lacks a saddle point, i.e., it is qualitatively different from any realistic system, which always exhibits a saddle. The singular model results in a temperature-dependent prefactor in the entire range of dissipation while any regular model leads to a temperature-independent prefactor for not too low dissipation.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.344896
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  • 2
    Electronic Resource
    Electronic Resource
    Enhancement of magnetoresistance in Co(11¯00)/Cr(211) bilayered films on MgO(110) : The 40th annual conference on magnetism and magnetic materials (1996)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 79 (1996), S. 6533-6535 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Epitaxial Co/Cr bilayered films have been successfully grown on the MgO(100) and MgO(110) substrates by molecular-beam epitaxy. According to the reflection high-energy electron-diffraction and x-ray-diffraction measurements the crystal structure of the film depends on orientation of the buffer and substrate. Epitaxial growth of biaxial Co(112¯0)/Cr(100) on MgO(100) substrate and of uniaxial Co(11¯00)/Cr(211) on MgO(110) substrate has been confirmed. The anisotropy magnetoresistance (AMR) is strongly influenced by the orientation of the Cr buffer. In Co(112¯0)/Cr(100) on MgO(100) AMR is isotropic for all in-plane fields. However, for Co(11¯00)/Cr(211) on MgO(110) we observed enhancement of AMR along the easy axis for temperatures below 150 K, while along the hard axis AMR has a local maximum at about 150 K. The easy axis data suggest that the longitudinal spin density wave of Cr and the crystal anisotropy of Co on Cr(211) plane dominate the enhancement of the AMR. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.361937
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  • 3
    Electronic Resource
    Electronic Resource
    Multilevel master equation for bicrystal clusters : The 40th annual conference on magnetism and magnetic materials (1996)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 79 (1996), S. 4919-4921 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A bicrystal film is modeled as an ensemble of clusters of four particles which interact via short-range exchange coupling. Their easy axes are oriented pairwise along two randomly chosen orthogonal directions and the relaxational dynamics of the resultant clusters are described in terms of a multilevel master equation. The randomly deposited bicrystal film is compared with a randomly deposited film of uniaxial clusters. The relaxational properties of the entire array are determined by the easy axes arrangement and by the nature of coupling within the cluster. In particular, for ferromagnetic coupling the occurrence probability of fully magnetized bicrystal cluster states is high and we propose that in conjunction with the highly isotropic coercivity this property leads to a sharp transition between film regions magnetized in opposite directions. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.361587
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  • 4
    Electronic Resource
    Electronic Resource
    Field orientations and sweep rate effects on magnetic switching of Stoner–Wohlfarth particles (1994)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 76 (1994), S. 1726-1732 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Field angles and sweep rate dependence of coercivity of the Stoner–Wohlfarth (S-W) particles are studied based on the decay-rate model. An analytic expression of the hysteresis loops based on the model is obtained as a function of applied field for various frequencies at various field angles with respect to the easy axis. Variation of the coercivities versus the sweep rate (measurement frequency), field angles, anisotropy constant, activation volume, and the combination thereof, and the distribution of easy axis, etc., have been obtained. Comparison with the thermal-equilibrium and S-W hysteresis loops are made. Coercivities of such a system generally increase with increasing sweep rate, anisotropy constant and activation volume, etc., hence decreases with increasing sweeping period. As a function of the field angles, the coercivity curve turns flat with increasing field angles and sweeping period.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.358424
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  • 5
    Electronic Resource
    Electronic Resource
    Temperature dependence of switching field distribution : 38th Annual Conference on Magnetism and Magnetic Materials (1994)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 75 (1994), S. 5897-5899 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The peak value of switching field distribution χmax, coercivity Hc, and saturation magnetization Ms are measured as functions of temperature T in Co-γ-Fe2O3 and γ-Fe2O3 powders. It is found that χmax has a maximum at T=Tp and evidence is presented also for the existence of a theoretically predicted minimum at T=Tm〈Tp. Coercivity is decreasing with T. For Ba-ferrite platelets we find that Hc has a maximum at T=T˜p and a minimum at T=T˜m≈Tp, where χmax has a local maximum. The possible origin of this unusual behavior is discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.355553
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  • 6
    Electronic Resource
    Electronic Resource
    Relaxation in magnetic continua : 38th Annual Confrerence on Magnetism and Magnetic Materials (1994)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 75 (1994), S. 5794-5796 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Within a recently developed axiomatic formalism for construction of stochastic field equations of motion a new form of the equation for damped dynamics of magnetization in ferromagnets is proposed. It takes into account spatially inhomogeneous dissipation due to exchange interactions and replaces the customary dissipation constant (due to relativistic effects) by a dissipation operator. This operator is constructed here by comparison of the resultant phenomenological spin wave spectra with results of microscopic calculations. Dynamic description of relaxation of the modulus of magnetization is discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.355565
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  • 7
    Electronic Resource
    Electronic Resource
    Henkel plots for thermally relaxing systems : The 41st annual conference on magnetism and magnetic materials (1997)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 81 (1997), S. 5230-5232 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Henkel and δM plots for an array of thermally relaxing, interacting uniaxial particles are analyzed using master equation formalism. It is found that the peaks of δM depend on coupling strength only indirectly, through the stability of the demagnetized and remanent states and that an unstable initial demagnetized state results in δM(approximate)0 even for a strongly coupled system. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.364476
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  • 8
    Electronic Resource
    Electronic Resource
    Structure and magnetic anisotropy of epitaxial fcc-Co(110) and hcp-Co(11¯00) films (1996)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 68 (1996), S. 2155-2157 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Fcc-Co(110) and hcp-Co(11¯00) films of 200 A(ring) thickness were grown on MgO(110) and bcc-Cr(211)/MgO(110), respectively, by the molecular beam epitaxy method. Reflection high energy diffraction was used to in situ characterize the crystal structure. Co films grown directly on MgO(110) were pseudomorphic fcc structure. Twofold symmetrical hcp-Co(11¯00) films on top of the bcc-Cr(211)/MgO(110) were grown and confirmed. The magneto-optical Kerr effect (MOKE) was used to investigate the magnetic anisotropy of these films. The magnetization of these samples was found to be in-plane. The magnetization of fcc-Co films has cubic symmetry with texture induced uniaxial anisotropy. For hcp-Co(11¯00)/bcc-Cr(211) bilayer films, the magnetization was strongly anisotropic, but independent of the thickness of the Cr layer. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.115616
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  • 9
    Electronic Resource
    Electronic Resource
    Hysteresis and limiting cycles in a high frequency ac field (2001)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 89 (2001), S. 7457-7459 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Numerical solutions of Brown's Fokker-Planck equation are used to analyze the response of a superparamagnetic particle to an ac applied field. The nature of the response is governed by the rate of intrawell relaxation processes: At low driving frequencies they maintain the system close to a quasistationary state, and the response is Markovian. By contrast, probability redistribution effects taking place at high frequencies lead to a non-Markovian response mode which displays memory phenomena. The high frequency limiting cycles are analyzed in detail, and the transition to conventional low frequency hysteresis loops is discussed. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1355347
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  • 10
    Electronic Resource
    Electronic Resource
    Macroscopic quantum tunneling in single domain magnetic particles (1988)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 63 (1988), S. 4234-4236 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Since the 1950's there have been a number of experimental observations involving small single domain (SD) magnetic particles ((approximately-less-than)200 A(ring) diameter) which have been attributed to what we'd today call "macroscopic quantum tunneling'' (MQT) of the magnetization in its switching from one easy axis direction to another. A comprehensive study of this phenomenon is not only of great interest for the sake of fundamental physics: It is of utmost practical importance in that MQT sets a limit on the lifetime of information storage on magnetic tapes and films. In this paper we present a brief summary of some of the latest results of our theoretical and experimental studies of this phenomenon.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.340216
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