Relaxation Phenomena in Ferrites

In a recent paper, Gait 1 ' 2 and Wijn and van der Heidc3 have suggested a mechanism for the losses observed during ferromagnetic resonance and domain wall motion in single crystals of nickel ferrite having a small amount of divalent iron substituted for divalent nickel in the octahedral sites. It is supposed that each substitution of a divalent iron atom for a divalent nickel atom provides one 3d electron able to move from one to another of the various iron atoms on the octahedral sites. For convenience, we shall term such electrons the "free electrons". With the crystal magnetized in a particular direction, these free 3d electrons will always so arrange themselves as to minimize the free energy of the crystal. The free energy, therefore, is going to depend upon the direction of magnetization because of this mechanism, in addition to its usual dependence upon the crystalline and shape anisotropy. It is clear that there will be an additional torque acting on the magnetization. In what follows, we shall assume that the free electrons cannot instantly assume the equilibrium arrangements specified by the motion of the 1 2 3