Magnetocrystalline anisotropy correlated negative anisotropic magnetoresistance in epitaxial Fe30Co70 thin films

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 cos 2 φ M and a series of MCA-dependent terms cos 2 n φ A ( n ≥ 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.