Annealing temperature dependence of non-collinear magnetic anisotropy in NiFe/NiO bilayers

Abstract

The unidirectional anisotropy and uniaxial anisotropy in exchange bias systems determine the effective field that governs magnetization precession, which is critical to magnetic applications. Research has found that a misalignment between unidirectional and uniaxial anisotropies may exist, i.e., non-collinear anisotropy, where the intrinsic mechanism and contributing factors are poorly reported. In this work, exchange-biased NiFe/NiO bilayers were fabricated by using magnetron sputtering. We investigated the effects of different annealing temperatures on the non-collinear anisotropy of the NiFe/NiO bilayers by measuring the in-plane angular dependence of the magnetic hysteresis loops and the ferromagnetic resonance. We found that the non-collinear angle β varied gradually from 0° to 45° with the variation in annealing temperature, which showed an asymmetric magnetization phenomenon. The competition between unidirectional and uniaxial anisotropy and the interfacial magnetic frustration play a major role in the asymmetric reversal phenomena in an antiferromagnet/ferromagnet system. Our results provide insight into the exchange-biased field and promote its application in spintronic devices.