Hysteresis Curves for a Dense Random Packing Model of an Amorphous Magnet with Random Uniaxial Anisotropy

Abstract

We consider the magnetic field behavior of a simple model for an amorphous ferromagnet with large random single ion anisotropy. The structure is represented by an interior portion of the dense random packing model of Finney. The spins are taken as classical unit vectors and are relaxed by a numerical procedure to direction which minimize applied field, anisotropy and near neighbor exchange energies. The hysteresis curves for the model resemble those found for TbFe 2 at low temperature, provided the anisotropy is about the same size as the exchange or larger. The coercivity increases abruptly with increasing anisotropy and then remains almost flat up to the “Ising” limit of infinite anisotropy. We have examined the energy of locally stable states and find that states of partially reversed moment, or states with spin glass character, are of markedly higher energy than aligned type states.