Anisotropic coercivity and the effects of interlayer exchange coupling in CoFeB/FeRh bilayers

In an amorphous CoFeB layer, coercivity becomes anisotropic with fourfold symmetry when the CoFeB layer exchange couples to an FeRh layer. The angular dependence of coercivity of the CoFeB layer coincides with the in-plane easy-axis direction of the FeRh layer and experiences a 45 degrees shift with the occurrence of a metamagnetic phase transition of the FeRh layer from antiferromagnetism at room temperature to ferromagnetism at 400 K. The intriguing phenomena are well reproduced by our unbiased Monte Carlo simulation. The interfacial exchange and anisotropy energies, as well as the interfacial magnetization in the CoFeB/FeRh bilayer, are disentangled to demonstrate the strong dependence of the imprinting of anisotropy in the CoFeB layer on the interfacial exchange coupling. The evolution of the easy-axis direction of the induced anisotropy arises from the reconstruction of the interfacial exchange energy profile accompanied with the change of the magnetic state of FeRh, which governs the magnetization reversal of the CoFeB layer at both branches. Moreover, the imprinting is further applicable for the uniaxial magnetocrystalline anisotropy. This work not only presents the possibility of directly duplicating anisotropy between dissimilar materials, but it also provides a powerful tool to probe the hidden magnetic structures and/or the properties of materials that have weak magnetism, such as antiferromagnetic materials.

Automated summary

Coercivity in an amorphous CoFeB layer becomes anisotropic with fourfold symmetry when exchange coupled with an FeRh layer. The angular dependence of coercivity coincides with the FeRh layer's in-plane easy-axis direction and shifts with FeRh's metamagnetic phase transition. This imprinting phenomenon is applicable for uniaxial magnetocrystalline anisotropy and provides a powerful tool to probe hidden magnetic structures and weakly magnetic materials.