Spin glass behavior in finite numerical samples

Abstract

The main points of a numerical simulation study of the spin glass transition in Ruderman-Kittel-Kasuya-Yosida (RKKY) systems are summarized. New results are also presented as follows. An investigation of the lifetime of spin freezing in a sample of 960 spins yields results which resemble qualitatively, if not quantitatively, the behavior of macroscopic systems. In the absence of anisotropy, a gradual spin freezing is found to set in at low temperatures when rotational decay of the Edwards-Anderson (EA) order parameter q is eliminated. However, this freezing exhibits no transition feature and is thought to be a finite sample effect. A study of 50 randomly selected ground states for a system of 500 spins is also presented. Evidence is given for a model of closely similar ground state pairs in which a small defect region occurs inverted in the two states concerned. Upper limit exchange barriers separating ground states are found to be substantially less than the mean thermal energy residing on the spins in the barrier region at reduced temperature T* = T G * in a number of cases. Thus, the possibility of barrier transitions, which underlie the observed decay of q, magnetic remanence, torque and EPR parameters, etc., in the spin glass state, is shown to be a natural feature of a disordered, exchange coupled spin system.