Fourfold anisotropic magnetoresistance of L1$_0$ FePt due to relaxation time anisotropy

TL;DR

This paper investigates the fourfold anisotropic magnetoresistance in L1$_0$ FePt films, revealing that it originates from relaxation time anisotropy caused by changes in the density of states near the Fermi level as magnetization rotates.

Contribution

The study demonstrates that fourfold AMR in FePt is due to relaxation time anisotropy, a universal property influencing various anisotropic phenomena in ferromagnetic metals.

Findings

Fourfold AMR depends only on magnetization direction, not current orientation.

Relaxation time anisotropy arises from density of states variation near the Fermi energy.

Universal property affecting multiple anisotropic physical properties.

Abstract

Experimental measurements show that the angular dependence of the anisotropic magnetoresistance (AMR) in L1$_0$ ordered FePt epitaxial films on the current orientation and magnetization direction is a superposition of the corresponding dependences of twofold and fourfold symmetries. The twofold AMR exhibits a strong dependence on the current orientation, whereas the fourfold term only depends on the magnetization direction in the crystal and is independent of the current orientation. First-principles calculations reveal that the fourfold AMR arises from the relaxation time anisotropy due to the variation of the density of states near the Fermi energy under rotation of the magnetization. This relaxation time anisotropy is a universal property in ferromagnetic metals and determines other anisotropic physical properties that are observable in experiment.