Exchange bias phenomena in ferrimagnetic based bilayers

We present positive and negative exchange bias (EB) phenomena observed in t wo ferrimagnetic-based amorphous bilayers systems: FeSn/FeGd and FeGd/TbFe. In both cases, magnetization measurements exhibit a shift of the loop of o ne of the ferrimagnetic layer towards a positive or negative field. In FeSn /FeGd, the coupling at the interface between the net magnetization of the t wo layers is antiferromagnetic, which leads to a positive shift. However in FeGd/TbFe bilayers, the coupling is ferromagnetic and the shift is negativ e. The EB phenomenon is attributed to the occurrence of a magnetic domain w all present at the interface, which can be "compressed" or "decompressed" b y an external applied field. A simple model based on the competition betwee n the Zeeman energy and the interface exchange interaction energy permits a good quantitative evaluation of the observed EB fields. (C) 2001 American Institute of Physics.