Dipolar ordering of random two-dimensional spin ensemble

TL;DR

This paper investigates the conditions under which two-dimensional ensembles of magnetic dipoles exhibit in-plane superferromagnetic ordering, identifying critical concentrations and temperature effects through theoretical analysis.

Contribution

It provides a theoretical framework for understanding dipolar ordering in 2D magnetic nanoparticle ensembles, including critical surface concentrations and temperature-dependent behavior.

Findings

Dipolar in-plane superferromagnetic ordering occurs above 0.24 surface concentration.

Critical concentration for random easy axis is 0.65 at zero temperature.

Ensemble with Ising spins orders near the Curie temperature.

Abstract

We theoretically study the randomly positioned two-dimensional system of interacting magnetic dipoles representing the monolayer arrays of single-domain particles. It is showed the onset of the dipolar in-plane superferromagnetic ordering of Ising spins at the surface concentrations of nanoparticles above 0.24. The critical concentration of particles with random easy axis arrangement at zero temperature is 0.65. It is demonstrated that the ensemble with Ising arrangement of spins is ordered at high temperatures close to a particle Curie point.