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

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.