Anomalies in the Relaxation of Small Magnetic Particles at Very Low Temperatures

TL;DR

This study investigates the magnetization relaxation behavior of small gamma-Fe2O3 particles at very low temperatures, revealing a minimum around 150 mK that suggests a transition between thermal and quantum relaxation mechanisms.

Contribution

It provides experimental data on magnetic relaxation in small particles at millikelvin temperatures, highlighting a possible crossover between thermal and quantum regimes.

Findings

Relaxation rate shows a minimum at ~150 mK.

Evidence of a transition between thermal and quantum relaxation.

Data extends understanding of magnetic dynamics at ultra-low temperatures.

Abstract

The magnetization relaxation rate of small gamma-Fe2O3 particles dispersed in a silica matrix has been measured from 60 mK to 5 K. It shows a minimum around 150 mK, that can be discussed in terms of either thermal or quantum relaxation regime.