The influence of the interfacial FeMn insertion layer on the pinning effect of IrMn/CoFe exchange coupled bilayers

The exchange bias and thermal stability of CoFe/IrMn films with and without thin FeMn layer at the interface were investigated. Very thin FeMn insertion layer was found to increase the pinning field largely. An optimum pinning field of ∼220 Oe was obtained for the film CoFe (100 A)/FeMn (1.5 A)/IrMn (70 A), while only 140 Oe was obtained for the film CoFe (100 A)/IrMn (70 A). Their coercivities were not much different. The two films' pinning field dependences of temperature were also almost the same and their blocking temperatures were both about 250 deg. C. This is ascribed that the local structure deformations at the interface of CoFe/IrMn increase the net spins of the interfacial antiferromagnetic atoms, and hence the exchange bias strength