Large Exchange Bias IrMn/CoFe for Magnetic Tunnel Junctions

Abstract

We report on the enhancement of the exchange field, Hex , in IrMn/CoFe systems as a result of the application of field annealing procedures. The exchange field is enhanced up to a 37% on application of a 2 Tesla field for 90 minutes at 225degC. This setting process improves the magnitude of H_EX without significant changes in the coercivity, H_C, or the median blocking temperature. The sample with largest exchange bias field measured, 3.7 kOe and H_C = 0.2 kOe at 20degC, seems to have the largest ratio of H_EX to H_C ever reported for an IrMn/CoFe exchange bias system. This makes these structures good candidates as pinned layers in magnetic tunnel junctions. The samples show good thermal stability with median blocking temperatures up to 200degC. The results also indicate that the improvement in the quality of the interfaces via the degree of alignment of the interfacial spins improves the coupling across the interface and hence the magnitude of the exchange bias field.