We describe the factors which control the measured value of exchange bias (HEX) in bilayers consisting of sputtered metallic thin films of an antiferromagnet (AF) in contact with a ferromagnetic (F) layer. Experimental measurements show that the value of HEX is determined by the grain volume distribution which limits the exchange bias via small grains which are thermally unstable, and large grains which cannot be set when the system is field annealed to set the AF at temperatures below TN. All the results are interpreted in terms of a granular model where the energy barrier to reversal within the AF is grain volume dependent. We show how this affects setting in metallic AFs at T<TN. We have also found that exchange bias is moderated by disordered spins at the F/AF interface. These spins can be ordered at low temperatures and by field annealing. Ordering of interfacial spins leads to an increase in HEX of up to 30%.
|Publication status||Published - 2008|
- Polycrystalline films
- Grain size
- thin film