Fourfold anisotropic magnetoresistance in FeCo and Fe₄N

Abstract The anisotropic magnetoresistance (AMR) of FeCo and Fe 4 N have been investigated using the spin-polarized full-relativistic Korringa-Kohn-Rostoker (SPR-KKR) method. The angular dependence of the magnetoresistivity was calculated where the atomic anti-site disorder in FeCo and the temperature effect in Fe 4 N were modeled by the coherent potential approximation (CPA). In addition to the twofold term in the AMR effect, the fourfold term appears when the degree of disorder decreases or temperature reduces and is independent of the electric current direction. We argue that the fourfold AMR does not necessitate tetragonal distortion and arises from the fourfold symmetry of the density of states at the Fermi surface induced by the magnetization rotation. At the same time, we show that the ratio between the fourfold and twofold terms can be tuned by properly setting the direction of the current. Our work provides an important clue to understanding AMR and its variations under the different magnetic fields and current directions.