Magnetic anisotropy problems

Henceforth we assume that the dominant process driving the m netic relaxation is reorientational diffusion. To calculate the ESR spectrum for ions of high magnetic anisotropy in viscous systems, which in general show an absorption line which covers some hundreds of gauss, it is necessary to take into accoimt some special aspects of the problem. 

The present most challenging problem of nanocomposite materials is their comparatively low coercivity. Recent values of the coercivities of isotropic magnets are presented in fig. 25. As seen, most of these magnets have coercivities less than 400 kA/m, except for some of the recently developed high-coercive powders. The values of coercivity are still comparatively small for industrial applications. Substitution of Dy or Tb for Nd is one way to increase the magnetic anisotropy of the main phase, and that has been tried by some groups (Coehoorn et al. 1989, Kanekiyo et al. 1993). These improvements, however, are at the expense of the magnetization and loop squareness. 

For many problems treating magnetic anisotropy effects and the magnetic relaxation of a rotating cluster in a magnetic field the phenomenological Hamiltonian... 

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