Exchange bias phenomena in ferrimagnetic based bilayers

We present positive and negative exchange bias (EB) phenomena observed in two ferrimagnetic-based amorphous bilayers systems: FeSn/FeGd and FeGd/TbFe. In both cases, magnetization measurements exhibit a shift of the loop of one of the ferrimagnetic layer towards a positive or negative field. In FeSn/FeGd, the coupling at the interface between the net magnetization of the two layers is antiferromagnetic, which leads to a positive shift. However in FeGd/TbFe bilayers, the coupling is ferromagnetic and the shift is negative. The EB phenomenon is attributed to the occurrence of a magnetic domain wall present at the interface, which can be 'compressed' or 'decompressed' by an external applied field. A simple model based on the competition between the Zeeman energy and the interface exchange interaction energy permits a good quantitative evaluation of the observed EB fields. [copyright] 2001 American Institute of Physics