Exchange bias investigations in FeMn based multilayers

We have carried out a systematic investigation of the development of exchange bias in an NiFe/FeMn/NiFe trilayer and in a trilayer with a nonmagnetic interlayer, in order to understand the development of bias in FeMn-based rf magnetron-sputtered multilayers. The trilayer shows two bias loops corresponding to the two NiFe layers where the seed layer shows a greater bias. The bias shows the expected 1/t variation with increasing seed layer thickness. The bias for the top NiFe layer of 5 nm constant thickness increases initially in the 2-6-nm range to reach a maximum value, and thereafter shows a surprising increase in bias at larger seed-layer thicknesses. The introduction of an Al layer of increasing thickness at the top FeMn surface causes the vanishing of the bias for the top NiFe layer and an increase in bias for the seed layer up to 1-nm thickness of Al layer and a decrease thereafter. The seed layer interestingly shows greater bias when an Al layer is present.