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  • 1
    Electronic Resource
    Electronic Resource
    Quantum dynamical calculations in clusters of spin 1/2 particles: Resonant coherent quantum tunneling on the magnetization reversal : The 40th annual conference on magnetism and magnetic materials (1996)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 79 (1996), S. 6110-6112 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We investigate the reversal of magnetization and the coherence of tunneling when an external magnetic field is rotated instantaneously in systems of a few (N) spin 1/2 particles described by an anisotropic Heisenberg Hamiltonian at T=0. The temporal evolution is calculated by a numerically exact solution of the time-dependent Schrödinger equation, and the mean value in time of each spin component is computed as a function of the magnetic field. The correlation function and the spectrum are analyzed in terms of the macroscopic quantum coherence. Our calculations demonstrate that this model for small (N〈11) magnetic particles exhibit collective tunneling of the magnetization only for some specific resonant values of the applied magnetic field, at variance with the Stoner–Wohlfarth model. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.362103
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    Paper (German National Licenses)
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  • 2
    Electronic Resource
    Electronic Resource
    Nonhomogeneous magnetization reversal in 2D Ising 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. 6019-6021 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We have performed Monte Carlo simulations on 2D circular Ising clusters, studying the distribution of the magnetization within the cluster as well as the magnetization reversal process when an applied external field is suddenly changed. We have shown that for highly anisotropic systems (the Ising-like limit), the magnetization reversal process is not uniform in a wide range of temperatures. Spins having a lower coordination at cluster edges drive the reversal process, acting as nucleation centers. We have found that there is a connection between the roughness transition temperature and the differences in the time evolution patterns of the magnetization. Our simulations agree with experimental results on magnetization reversal of single domain particles. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.362139
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    Paper (German National Licenses)
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  • 3
    Electronic Resource
    Electronic Resource
    Field-tuned quantum tunneling of the magnetization : The 7th joint MMM-intermag conference on magnetism and magnetic materials (1998)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 83 (1998), S. 6937-6939 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The response of the magnetization to a time-dependent applied magnetic field in single-spin models for uniaxial magnets is studied. We present staircase magnetization curves obtained from the numerically exact solution of the time-dependent Schrödinger equation. Steps are shown to correspond to field-tuned quantum tunneling between different pairs of nearly degenerate energy levels. We investigate the role played by different terms that allow for tunneling processes: transverse fields and second-order and fourth-order transverse anisotropies. Magnetization curves for nonsaturated initial states and for excited initial states showing steps when the field decreases in absolute value are also presented. These results are discussed in relation to recent experiments on high-spin compounds. © 1998 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.367531
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    Paper (German National Licenses)
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