Study of exchange anisotropy in NiFe/NiMn and NiFe/IrMn exchange coupled films

Abstract

Exchange anisotropy in NiFe/NiMn and NiFe/IrMn exchange coupled films was studied as a function of temperature using vibrating sample magnetometry. The exchange field was measured using three different methods: (1) as a shift of the hysteresis loop measured in an external field applied parallel to the exchange field direction; (2) calculated from the initial susceptibility in the field applied perpendicular to the exchange field; and (3) calculated from the shift of minor reversible hysteresis loops measured in external fields applied in a few different directions close to the perpendicular to the exchange field. The values of the exchange field in NiFe/NiMn samples measured using methods 2 and 3 were similar and approximately twice as high as the values measured using method 1. For the NiFe/IrMn samples methods 2 and 3 gave exchange field values slightly exceeding the values obtained using method 1. The results are explained using a model in which it is assumed that the interfacial interactions between antiferromagnetic and ferromagnetic layers induce unidirectional and uniaxial anisotropy in the ferromagnetic layer. The temperature dependence of induced interfacial uniaxial anisotropy was calculated from the experimental data. For the NiFe/NiMn samples, the temperature dependence of the induced uniaxial anisotropy was significantly different from that of the unidirectional anisotropy.