Spin wave excitations and the magnetization curve of amorphous ferromagnets

Abstract

Within the Heisenberg model it is studied, how the magnetic excitations and the magnetization curve of an amorphous ferromagnet depend on the exchange integralJ(r). For the “relaxed” structural model of L. von Heimendahl, consisting ofN=888 sites, the density of spin wave states is calculated by means of a continued fraction algorithm, using various model assumptions on the radial dependence ofJ(r). Although it is assumed thatJ(r) is different from zero only within the “nearest neighbour region” of the radial distributiong(r), the density of spin wave states and the critical temperature are strongly influenced by a positive or negative derivative ofJ(r) in this region. However, the magnetization curves, which are calculated in the Tyablikov decoupling approximation fors=1/2, show only a weak flattening, compared with the idealfcc case, when presented overT/Tc. The calculated low-temperature behaviour of the magnetization is compared with recent experiments on ferromagnetic metglasses, and it is found that a description with localized spins and a short-range Heisenberg interaction should be much better for these systems than for the corresponding crystalline metals.