Ground State of an Ising Antiferromagnet with a Dense Random Packing Structure

Abstract

Although the existence of ferromagnetism in amorphous materials is well confirmed both from the theoretical and the experimental point of view the appearance of antiferromagnetism in such substances is dubious. First a simple theory of amorphous antiferromagnetism was given using the molecular field theory.1,2 The structural disorder was simulated by a sublattice model, i.e., the spins were arranged on lattice points with the antiferromagnetic exchange interactions between them fluctuating randomly. However, in this model all nearest neighbors of a given spin belong to the other sublattice. This assumption is an inadmissable restriction, since in real amorphous systems it is impossible to surround a plus spin by minus spins only or vice versa. Amorphous antiferromagnetism can be disfavored by having the so-called misfit structure, which also occurs in some crystalline antiferromagnets (e.g., fcc lattice with nearest neighbor interaction).3–5 For an improved description random packing of hard spheres, which succeededs in interpreting the radial distribution functions of amorphous systems, are more suitable structure models. Recently there are first attempts to investigate magnetic properties using these models.6–8