Magnetic relaxation and dipole-coupling-induced magnetization in nanostructured thin films during growth: A cluster Monte Carlo study

TL;DR

This study models the magnetic behavior of nanostructured thin films during growth, revealing how dipole interactions and anisotropy influence magnetic order and relaxation at various coverages.

Contribution

It introduces a cluster Monte Carlo method that accounts for coherent magnetization changes, enabling analysis of magnetic transitions during film growth.

Findings

Dipole interactions induce magnetic order below the percolation threshold.

Anisotropy causes blocking temperatures of 10-100 K.

Dipole coupling slightly slows magnetic relaxation.

Abstract

For growing inhomogeneous thin films with an island nanostructure similar as observed in experiment, we determine the nonequilibrium and equilibrium remanent magnetization. The single-island magnetic anisotropy, the dipole coupling, and the exchange interaction between magnetic islands are taken into account within a micromagnetic model. A cluster Monte Carlo method is developed which includes coherent magnetization changes of connected islands. This causes a fast relaxation towards equilibrium for irregularly connected systems. We analyse the transition from dipole coupled islands at low coverages to a strongly connected ferromagnetic film at high coverages during film growth. For coverages below the percolation threshold, the dipole interaction induces a collective magnetic order with ordering temperatures of 1 - 10 K for the assumed model parameters. Anisotropy causes blocking temperatures of 10 - 100 K and thus pronounced nonequilibrium effects. The dipole coupling leads to a somewhat slower magnetic relaxation.