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

We report on the experimental and theoretical studies of cooling field (H(FC)) and temperature (T) dependent exchange bias (EB) in Fe(x)Au(1 − x)/Fe(19)Ni(81) spin glass (SG)/ferromagnet (FM) bilayers. When x varies from 8% to 14% in the Fe(x)Au(1 − x) SG alloys, with increasing T, a sign-changeable exchange bias field (H(E)) together with a unimodal distribution of coercivity (H(C)) are observed. Significantly, increasing in the magnitude of H(FC) reduces (increases) the value of H(E) in the negative (positive) region, resulting in the entire H(E) ∼ T curve to move leftwards and upwards. In the meanwhile, H(FC) variation has weak effects on H(C). By Monte Carlo simulation using a SG/FM vector model, we are able to reproduce such H(E) dependences on T and H(FC) 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.