Intrinsic Mechanism for Anisotropic Magnetoresistance and Experimental Confirmation in CoxFe1−x Single-Crystal Films

Abstract

Using first-principles transport calculations, we predict that the anisotropic magnetoresistance (AMR) of single-crystal Co x Fe 1−x alloys is strongly dependent on the current orientation and alloy concentration. An intrinsic mechanism for AMR is found to arise from the band crossing due to magnetization-dependent symmetry protection. These special k points can be shifted towards or away from the Fermi energy by varying the alloy composition and hence the exchange splitting, thus allowing AMR tunability. The prediction is confirmed by delicate transport measurements, which further reveal a reciprocal relationship of the longitudinal and transverse resistivities along different crystal axes.

Temperature dependence of intrinsic and extrinsic contributions to anisotropic magnetoresistance

“…The existence of the intrinsic contribution has also been investigated experimentally. Hupfauer et al demonstrated the crystalline AMR effect, originating from the difference in electronic density, through its magnetization orientation 19 , and Zeng et al reported the intrinsic contribution caused by the magnetization-direction-dependent band crossing effect 20 .…”

Anisotropic magnetoresistance: A 170-year-old puzzle solved

“…Zeng et al [3] used a sophisticated first-principles code designed to calculate the transport properties in the presence of impurities, spin-orbit interaction, as well as magnetic, thermal and alloy disorder [7]. The excellent agreement of the calculated results with the AMR measured at Fudan and Argonne supports the validity of the method.…”

“…Alloys of the transition metals Fe, Ni, and Co are the materials of choice because they combine a large AMR ratio with other convenient properties [2]. In a convergence and culmination of methods and ideas developed in the past decades, a collaboration led by Zhe Yuan from Beijing Normal University (theory) and Yizheng Wu from Fudan University (experiments) recently solved the conundrum of the AMR for the generic alloy Co x Fe 1−x [3].…”

“…Ref. [3]'s breakthrough is the subsequent analysis of the numerical results in terms of the band structure topology as a function of applied magnetic field, current direction, and alloy concentration. The authors identified not just points, but full circles of crossing bands or "nodal lines" in reciprocal space when the magnetization is normal to a mirror plane (blue lines in Figure 1(a)).…”

“…Zeng et al [3] not only provide a satisfactory explanation of the AMR, but also solicit new questions and research directions:…”