52 research outputs found
Power law analysis for temperature dependence of magnetocrystalline anisotropy constants of NdFeB magnets
Phenomenological analysis for the temperature dependence of the
magnetocrystalline anisotropy (MA) in rare earth magnets is presented. We
define phenomenological power laws applicable to compound magnets using the
Zener theory, apply these laws to the magnetocrystalline anisotropy constants
(MACs) of NdFeB magnets. The results indicate that the MACs obey the
power law well, and a general understanding for the temperature-dependent MA in
rare earth magnets is obtained through the analysis. Furthermore, to examine
the validity of the power law, we discuss the temperature dependence of the
MACs in DyFeB and YFeB magnets as examples wherein it is
difficult to interpret the MA using the power law.Comment: 5pages, 6 figure
Analytic Expression for Magnetic Activation Energy
We theoretically investigate the magnetic activation energy of permanent
magnets. Practically, it is widely used in a phenomenological form as
where is the activation energy in the absence of an
external magnetic field , is a real parameter, and is
defined by the equation . We derive the general
and direct expressions for these phenomenological parameters under the
restriction of uniform rotation of magnetization and on the basis of the
perturbative theory with respect to . Further,we apply our
results to NdFeB magnets and confirm the validity of the proposed
method by comparing with the Monte Carlo calculations.Comment: 8 pages, 2 figure
Decoherence processes of a quantum two-level system coupled to a fermionic environment
We study decoherence processes of an S = 1/2 localized spin coupled to
conduction band electrons in a metal or a semiconductor via an Ising-like
interaction. We derive master equations for the density matrix of the localized
spin, by tracing out all degrees of freedom in the conduction electron system
based on the linked-cluster-expansion technique. It is found that the
decoherence occurs more rapidly for the metallic case than for semiconducting
case.Comment: to appear in J. Appl. Phy
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