Influence of Concentration Fluctuations on Relaxation Processes in Spin Glasses

Julia Wagner,Wolfgang Häußler,Peter Böni,Andreas Bauer,Stephen Shapiro,Olaf Holderer

doi:10.3390/qubs2040026

Abstract

Using the unique combination of atomically resolved atom probe tomography (APT) and volume averaged neutron (resonance) spin echo (NRSE and NSE) experiments, the influence of nano-scaled clusters on the spin relaxation in spin glasses was studied. For this purpose, the phase transition from the paramagnetic phase to the spin glass phase in an Fe-Cr spin glass with a composition of Fe 17 . 8 Cr 82 . 2 was studied in detail by means of NRSE. The microstructure was characterised by APT measurements, which show local concentration fluctuations of Fe and Cr on a length scale of 2 to 5 nm, which lead (i) to the coexistence of ferro- and anti-ferromagnetic clusters and (ii) a change of the magnetic properties of the whole sample, even in the spin glass phase, where spins are supposed to be randomly frozen. We show that a generalized spin glass relaxation function, which was successfully used to describe the phase transition in diluted spin glasses, can also be used for fitting the spin dynamics in spin glasses with significant concentration fluctuations.

Highlights

Spin glasses possess no long-range magnetic order due to frustrated magnetic interactions and disorder, which leads to stochastically oriented magnetic moments
We show that a generalized spin glass relaxation function, which was successfully used to describe the phase transition in diluted spin glasses, can be used for fitting the spin dynamics in spin glasses with significant concentration fluctuations
We study the relation between microstructure leading to magnetically ordered clusters and the averaged spin relaxation in an Fe-Cr sample, which shows a temperature driven phase transition to a cluster spin glass (SG) phase

Summary

Introduction

Spin glasses possess no long-range magnetic order due to frustrated magnetic interactions and disorder, which leads to stochastically oriented magnetic moments. Phase transitions in spin glasses occur at temperatures below 60 K. The disorder in the system at high temperatures, which is typically paramagnetic, reappears at low temperatures in a frozen state. Due to the frustration of the magnetic states in the spin glass phase, slow decay processes on large time scales may be observable [1]. Muon spin relaxation (μSR) allows for extending the time scale to 1 μs [4]. Being a local probe μSR does not allow for obtaining information on the spatial correlations of the relaxation processes

Results

Discussion

Conclusion