Random Anisotropy Magnet at Finite Temperature

TL;DR

This study uses large-scale Monte Carlo simulations to investigate the finite-temperature behavior of a 2D random-anisotropy magnet, confirming the predicted spin-glass state and elucidating the nature of the freezing transition.

Contribution

It provides the first large-scale simulation evidence of the correlated spin-glass state and the freezing mechanism driven by random anisotropy energy barriers.

Findings

Reproduced the correlated spin-glass state predicted by theories.

Observed field-cooled and zero-field-cooled magnetization curves matching experiments.

Identified the freezing transition as due to anisotropy energy barriers, not random interactions.

Abstract

Abstract We present finite-temperature Monte Carlo studies of a 2D random-anisotropy magnet on lattices containing one million spins. The correlated spin-glass state predicted by analytical theories is reproduced in simulations, as are the field-cooled and zero-field-cooled magnetization curves observed in experiments. The orientations of lattice spins begin to freeze when the temperature is lowered. The freezing transition is due to the energy barriers generated by the random anisotropy rather than due to random interactions in conventional spin-glasses. We describe freezing by introducing the time-dependent spin-glass order parameter $q$ and the spin-melting time $\tau_{M}$ defined via $q=\tau_{M}/t$ above freezing, where t is the time of the experiment represented by the number of Monte Carlo steps.