期刊
NEW JOURNAL OF PHYSICS
卷 25, 期 2, 页码 -出版社
IOP Publishing Ltd
DOI: 10.1088/1367-2630/acb6e7
关键词
CoFeB/IrMn bilayer; interfacial exchange coupling; four-fold magnetic anisotropy
We observed a fourfold magnetic anisotropy induced by interfacial exchange coupling in ferromagnetic/antiferromagnetic bilayers, which can be nicely fitted by a phenomenological model. This additional anisotropy is caused by the presence of two types of antiferromagnetic domains, resulting in different effects on the magnetization.
Exchange bias (EB) occurring in ferromagnetic (FM)/antiferromagnetic (AFM) bilayers conventionally can lead to a unidirectional magnetic anisotropy (Keb) as well as an accompanied uniaxial magnetic anisotropy (Ku). We observed an additional fourfold magnetic anisotropy (K-4) induced by interfacial exchange coupling in amorphous CoFeB/epitaxial IrMn bilayers with an EB. Because of the combined effect of the three kinds of magnetic anisotropies, one-and two-step magnetic switching processes were observed at different magnetic field orientations, which usually appear in single-crystal FM layer with an intrinsic magnetocrystalline anisotropy but not in amorphous FM layer. The angular dependent magnetic switching fields can be nicely fitted by a phenomenological model based on domain wall nucleation and propagation with the in-plane K-4 along < 100 >. The ferromagnetic resonance measurements indicate that the specific strength of K-4 for EB along [100] is larger than that for EB along [110]. The induced K-4 can be understood by considering two types of AFM domains caused by both monatomic steps and defects and their induced net uncompensated spins along the in-plane < 100 > axes. The different dependence of K-4 on the EB direction are because of the different effects of growth magnetic field on the presence of AFM domains.
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