Phase diagram of dipolar-coupled XY moments on disordered square lattices

TL;DR

This study investigates how dilution and displacement disorder affect dipolar-coupled XY moments on square lattices, revealing that both types of disorder promote a microvortex phase at low temperatures.

Contribution

The paper introduces new order parameters and uses parallel tempering Monte Carlo simulations to map phase diagrams for disordered dipolar systems.

Findings

Both disorders lead to similar phase diagrams.

Disorder favors microvortex phase at low temperatures.

Flux closure explains the microvortex stabilization.

Abstract

The effects of dilution disorder and random-displacement disorder are analyzed for dipolar-coupled magnetic moments confined in a plane, which were originally placed on the square lattice. In order to distinguish the different phases, new order parameters are derived and parallel tempering Monte Carlo simulations are performed for a truncated dipolar Hamiltonian to obtain the phase diagrams for both types of disorder. We find that both dilution disorder and random-displacement disorder give similar phase diagrams, namely disorder at small enough temperatures favors a so-called microvortex phase. This can be understood in terms of the flux closure present in dipolar-coupled systems.