Exchange Coupling and Decoupling in a Nanocomposite Spin System

TL;DR

This paper investigates how exchange coupling and decoupling occur in a nanocomposite spin system using Monte Carlo simulations of a 3D Heisenberg model, revealing key factors influencing magnetic behavior.

Contribution

It introduces a bottom-up simulation approach for complex spin lattices, differing from conventional micromagnetism methods, and explores the effects of various parameters on exchange phenomena.

Findings

Lower exchange constant Jab promotes decoupling.

Larger cluster spins d favor decoupling.

Lower temperature t enhances decoupling and two-stage demagnetization.

Abstract

We studied the exchange coupling and decoupling occurring in a nanocomposite spin system based on a 3D Heisenberg model by means of Monte Carlo numerical computation simulation. Different from conventional micromagnetism approach which usually adopts finite elements method to compute, in a top-down way, the magnetic property of micromagnetic ensemble in micron even nanometer scale, our approach in this paper is peculiar to the structure of a complex spin lattice, i.e. two species of spins building up from single spin to cluster spins in a bottom-up way. The simulation revealed the influence of exchange coupling constant Jab, the size of cluster spins d and system reduced temperature t upon the exchange coupling and decoupling between component spin phases of a nanocomposite magnets, respectively. Smaller value of Jab, larger d and lower temperature t usually lead to the decoupling of originally exchange-coupled component phases and the occurrence of a characteristic two-stage shoulder with an inflexion on the demagnetization curve. The results reported in this paper are of, to some extent, universality and applicable to other dual-phase magnetic systems since our simulation simply focus on a pure duplex spin system rather than a specific material and all physical variables were treated in a reduced form.