Classical and quantum magnetisation reversal studied in single nanometer-sized particles and clusters using micro-SQUIDs

TL;DR

This paper reviews experimental studies on magnetisation reversal in nanometer-sized particles, highlighting the transition from classical thermal activation to quantum tunnelling at very low temperatures using micro-SQUID measurements.

Contribution

It provides experimental evidence of quantum tunnelling effects in nanomagnets, bridging the gap between classical and quantum magnetic behaviour in individual nanoparticles.

Findings

Magnetisation reversal in small nanoparticles follows thermal activation at higher temperatures.

Deviations from classical models occur below 0.4 K, indicating quantum tunnelling.

Results support the theory of macroscopic quantum tunnelling in low dissipation regimes.

Abstract

Recent progress in experiment on quantum tunnelling of the magnetic moment in mesoscopic systems will be reviewed. The emphasis will be made on measurements of individual nanoparticles. These nanomagnets allow one to test the border between classical and quantum behaviour. Using the micro-SQUID magnetometer, waiting time, switching field and telegraph noise measurements show unambiguously that the magnetisation reversal of small enough single crystalline nanoparticles is described by a model of thermal activation over a single-energy barrier. Results on insulating BaFeO nanoparticles show strong deviations from this model below 0.4 K which agree with the theory of macroscopic quantum tunnelling in the low dissipation regime.