Bulk and interfacial effects in exchange bias systems

In this work we report on an extensive and detailed study of exchange bias systems consisting of two ferromagnetic layers deposited with an antiferromagnetic layer of IrMn between them. Systems with two different ferromagnetic layers have been studied in which sample 1 had CoFe layers of different thicknesses and sample 2 had not only ferromagnetic layers of different thicknesses but also the composition of the upper ferromagnetic layers was changed from CoFe to NiFe. In both the samples the antiferromagnetic layer thickness was maintained constant at 5 nm, NiCr seed and capping layers (5 nm) were used on all samples. Such a system is of considerable interest as the properties of each ferromagnetic layer are affected by the same antiferromagnet. However differences in behaviour will occur due to the nature of the interfaces between the different layers as well as other parameters such as the ferromagnetic layer thickness. We have conducted a study of thermal activation effects in these systems where both or a single ferromagnetic layer can be reversed whilst the system is heated. We find that we can differentiate between bulk and interface effects indicating that the role of spin disorder at the interface is crucial in determining the final value of the exchange bias.