Magnetocrystalline anisotropy correlated negative anisotropic magnetoresistance in epitaxial Fe30Co70 thin films

Abstract

We report on the magnetoresistance in different crystallographic directions of epitaxial ferromagnetic Fe₃₀Co₇₀ thin films with magnetization rotated in the film plane. A negative single crystal anisotropic magnetoresistance (SCAMR) is found when the current is along the easy magnetization axis [110], and the SCAMR can be tuned to the conventional positive one when the current flows along the hard magnetization axis [100]. This finding is explained comprehensively by a magnetocrystalline anisotropy (MCA) symmetry-adapted model expanded along the easy magnetization direction, with which the SCAMR can be represented as a MCA-independent conventional term $\text{cos}\hspace{0.17em}2{\phi }_M$ and a series of MCA-dependent terms $\text{cos}\hspace{0.17em}2n{\phi }_A$ ($n\ge 1$ ). The results show that the MCA-dependent twofold term contributes to the negative SCAMR, which cannot be used as a fingerprint of the half-metallicity. Our finding provides an approach to understand and design the magnetoresistance with ferromagnets by MCA.