Dipolar interaction and incoherent quantum tunneling: a Monte Carlo study of magnetic relaxation

TL;DR

This study uses Monte Carlo simulations to analyze magnetic relaxation in systems of localized spins with dipolar interactions, revealing a $ oot t$ decay at short times and an extended relaxed zone at long times, aligning with experimental data.

Contribution

It provides a detailed Monte Carlo analysis of quantum tunneling-driven magnetic relaxation considering dipolar interactions, extending understanding of relaxation dynamics in molecular magnets.

Findings

Magnetization decreases as $ oot t$ at short times.

Relaxation at long times involves an extended relaxed zone.

Results agree with experimental data on Fe_8 molecular clusters.

Abstract

We study the magnetic relaxation of a system of localized spins interacting through weak dipole interactions, at a temperature large with respect to the ordering temperature but low with respect to the crystal field level splitting. The relaxation results from quantum spin tunneling but is only allowed on sites where the dipole field is very small. At low times, the magnetization decrease is proportional to $\sqrt{t}$ as predicted by Prokofiev and Stamp, and at long times the relaxation can be described as an extension of a relaxed zone. The results can be directly compared with very recent experimental data on Fe_8 molecular clusters.