Fourfold magnetic anisotropy varied by interfacial exchange coupling in epitaxial Fe/IrMn bilayers

We report variable in-plane fourfold magnetic anisotropy in epitaxial exchange-biased Fe/IrMn bilayers with different layer thicknesses. The fourfold magnetic anisotropy of the bilayers continuously decreases and even appears negative as the thickness of the Fe layer decreases, indicating a change in the easy axes from Fe 100 to Fe 110, which can be interpreted by the competition between the intrinsic magnetocrystalline anisotropy along Fe 100 and the extrinsic fourfold magnetic anisotropy along Fe 110 induced by the interfacial exchange coupling to IrMn. As the IrMn thickness increases, the fourfold magnetic anisotropy of the bilayers decreases rapidly from a value close to the intrinsic magnetocrystalline anisotropy of Fe and then gradually reaches saturation. The extrinsic fourfold magnetic anisotropy depends on the amount of the induced uncompensated IrMn spins near the edge of antiferromagnetic domains. In contrast, the exchange bias is determined by the net difference of the opposite uncompensated IrMn spins.