Nature of the spin-glass phase in dense packings of Ising dipoles with random anisotropy axes

TL;DR

This study uses Monte Carlo simulations to analyze the spin-glass phase in dense packings of Ising dipoles with random axes, revealing quasi-long-range order and specific finite-size effects.

Contribution

It provides new insights into the nature of the spin-glass phase in dense dipolar systems, showing evidence of quasi-long-range order and finite-size scaling behavior.

Findings

Existence of an equilibrium spin-glass phase below T_sg

Algebraic decay of the overlap parameter with system size

Evidence of quasi-long-range order in the spin-glass phase

Abstract

Using tempered Monte Carlo simulations, we study the the spin-glass phase of dense packings of Ising dipoles pointing along random axes. We consider systems of L^3 dipoles (a) placed on the sites of a simple cubic lattice with lattice constant $d$, (b) placed at the center of randomly closed packed spheres of diameter d that occupy a 64% of the volume. For both cases we find an equilibrium spin-glass phase below a temperature T_sg. We compute the spin-glass overlap parameter q and their associated correlation length xi_L. From the variation of xi_L with T and L we determine T_sg for both systems. In the spin-glass phase, we find (a) <q> decreases algebraically with L, and (b) xi_L/L does not diverge as L increases. At very low temperatures we find comb-like distributions of q that are sample-dependent. We find that the fraction of samples with cross-overlap spikes higher than a certain value as well as the average width of the spikes are size independent quantities. All these results are consistent with a quasi-long-range order in the spin-glass phase, as found previously for very diluted dipolar systems.