Giant anisotropy of magnetic damping in an epitaxial Cr/Fe bilayer with the absence of magnetocrystalline anisotropy

Magnetic damping is one of the most important parameters governing the critical current density for current-induced magnetization switching in spin-torque devices. The anisotropic nature of magnetic damping, influenced by both intrinsic and extrinsic factors, has been demonstrated in both theoretical and experimental studies. Nevertheless, understanding the underlying mechanisms of magnetic damping anisotropy, particularly in the bilayer structure of a ferromagnet and a nonmagnetic metal, remains an open challenge. In this study, we investigate the crystallographic dependence of magnetic damping in an epitaxial Cr/Fe bilayer, which has negligible magnetocrystalline anisotropy. We experimentally extracted the total damping by conducting frequency-dependent ferromagnetic resonance measurement at different in-plane angles. The observed damping reveals a strong angular dependence with an anisotropy of similar to 400% in the bilayer. All possible contributions to the total damping will be discussed carefully to clarify the origin of the profound damping anisotropy observed in our Cr/Fe bilayer.