Cooling field and temperature dependent exchange bias in spin glass/ferromagnet bilayers.

W B Rui,B You,W Zhang,Y Hu,A Du,J Du,M W Xiao,S M Zhou

doi:10.1038/srep13640

Abstract

We report on the experimental and theoretical studies of cooling field (HFC) and temperature (T) dependent exchange bias (EB) in FexAu1 − x/Fe19Ni81 spin glass (SG)/ferromagnet (FM) bilayers. When x varies from 8% to 14% in the FexAu1 − x SG alloys, with increasing T, a sign-changeable exchange bias field (HE) together with a unimodal distribution of coercivity (HC) are observed. Significantly, increasing in the magnitude of HFC reduces (increases) the value of HE in the negative (positive) region, resulting in the entire HE ∼ T curve to move leftwards and upwards. In the meanwhile, HFC variation has weak effects on HC. By Monte Carlo simulation using a SG/FM vector model, we are able to reproduce such HE dependences on T and HFC for the SG/FM system. Thus this work reveals that the SG/FM bilayer system containing intimately coupled interface, instead of a single SG layer, is responsible for the novel EB properties.

Highlights

H axis when FM/AFM systems are cooled below an Exchange bias (EB) blocking temperature (TB) under an external magnetic cooling field (HFC)[10,11]
Distinct from the AFM based systems, this study suggests that the EB effect and especially the sign-changeable behavior in the narrow T region just below TB in the spin glasses (SG)/FM bilayer systems may be inherent, and exists in all exchange biased SG/FM bilayers
Our work reveals that this reconfiguration can be controlled by HFC and behaves quite differently in different T regions

Summary

Introduction

H axis when FM/AFM systems are cooled below an EB blocking temperature (TB) under an external magnetic cooling field (HFC)[10,11]. A sign inversion of HE, i.e., a small positive EB, can be observed in a narrow T region just below TB for some EB systems[17,18] These abnormal phenomena are argued to be a result of the unidirectional coercivity (HC) enhancement along the HFC direction. Usadel and Nowak[24] have attempted to reproduce the EB phenomena in the SG/FM bilayer systems by applying an Ising model considering a short-range Gaussian distribution of interactions to simulate the SG material While they were able to predict the decrease in the magnitude of HE at low T when increasing HFC, the model failed to obtain the HE ∼ T behaviors as seen in Ref. 21–23. Distinct from the AFM based systems, this study suggests that the EB effect and especially the sign-changeable (positive EB) behavior in the narrow T region just below TB in the SG/FM bilayer systems may be inherent, and exists in all exchange biased SG/FM bilayers

Methods

Results

Conclusion