Anomalous exchange bias in Gd/Cr bilayer and Cr/Gd/Cr trilayers

Exchange bias has been observed in Gd/Cr bilayers and Cr/Gd/Cr trilayers systems in which the Curie temperature (T-C) of ferromagnetic Gd is less than the Neel temperature (T-N) of antiferromagnetic Cr. The exchange bias field H-E and coercivity H-C of the samples exhibit anomalous temperature dependence behavior in comparison with the conventional ferromagnet/antiferromagnet bilayers with T-C > T-N. As temperature increases, H-E increases monotonically until T-C, whereas H-C drops first and then goes up; finally, it disappears at T-C, which is attributed to the noncollinear interfacial exchange coupling between Gd and Cr. The results show that the exchange bias may exist in the AFM/FM bilayers regardless of the condition of T-C > T-N. (c) 2007 Elsevier B.V. All rights reserved.