Theory of spin glasses

TLDR

Classical calculations predict that as temperature approaches zero, the susceptibility and specific heat of spin glasses tend to constant values, though a quantum mechanical treatment is required at very low temperatures. The study proposes a new theory of dilute magnetic alloys (spin glasses) to explain the experimentally observed cusp in magnetic susceptibility. The theory posits that oscillating sign interactions between spins in the matrix produce no net ferro‑ or antiferromagnetism, but yield a ground state with randomly oriented spins. The model predicts a cusp in susceptibility at the critical temperature due to preferred spin orientations, which is smoothed when an external field is applied.

Abstract

A new theory of the class of dilute magnetic alloys, called the spin glasses, is proposed which offers a simple explanation of the cusp found experimentally in the susceptibility. The argument is that because the interaction between the spins dissolved in the matrix oscillates in sign according to distance, there will be no mean ferro- or antiferromagnetism, but there will be a ground state with the spins aligned in definite directions, even if these directions appear to be at random. At the critical temperature the existence of these preferred directions affects the orientation of the spins, leading to a cusp in the susceptibility. This cusp is smoothed by an external field. Although the behaviour at low t needs a quantum mechanical treatment, it is interesting to complete the classical calculations down to t=0. Classically the susceptibility tends to a constant value at t=0, and the specific heat to a constant value.