Oscillatory temperature dependence of exchange bias for Fe/Gd ferrimagnets

We investigated the exchange bias effect for Fe/Gd ferrimagnetic multilayers. Our results show that there is a -cosine type of oscillatory exchange bias with temperature for the [(Fe 4 nm/Gd 4 nm)(4)/Gd 16 nm] multilayer. For the first time, exchange bias was observed to oscillate between positive and negative fields with a period of approximately 130 K. In addition, the coercive field was observed to oscillate within itself for the same temperature range studied. We speculate that oscillatory exchange bias is related to the underlying magnetic phase diagram of the ferrimagnetic Fe/Gd multilayer. When the [(Fe 4 nm/Gd 4 nm)(4)/Gd 16 nm] system is cooled under a high magnetic field, negative exchange bias is forced to shift to positive values irregularly. Nevertheless the system shows oscillatory behaviour.