Fourfold magnetic anisotropy induced in CoFeB/IrMn bilayers by interfacial exchange coupling

Abstract

Exchange bias 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 (K4) induced by interfacial exchange coupling in amorphous CoFeB/epitaxial IrMn bilayers with an exchange bias (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 K4 along <100>. The ferromagnetic resonance measurements indicate that the specific strength of K4 for EB along [100] is larger than that for EB along [110]. The induced K4 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 K4 on the EB direction are because of the different effects of growth magnetic field on the presence of AFM domains.

The noncollinear interlayer coupling in NiFe/NiO/NiFe trilayers

“…The latter suggests that the antiferromagnetic spin structure can play a crucial role in modifying interlayer coupling [3]. Moreover, antiferromagnets (AFMs) have emerged as key materials in spintronic devices due to their unique features compared to FMs [4][5][6]. The propagation of spin currents through AFMs has a significant impact on spin transport properties and provides opportunities for the manipulation of spin-orbital torque (SOT) [7][8][9][10][11].…”