Tetragonal distortion modified magnetism and anomalous Hall effect of Mn₂CoAl Heusler alloys through Ar ion irradiation

Abstract

Tetragonal Heusler alloys are attracting more attention owing to their great scientific and technological interest in spintronics. However, the crystal structures of most Heusler alloys are cubic. One feasible method to obtain tetragonal Heusler alloy is to manipulate the out-of-plane distortion of cubic Heusler alloys. In this work, we report the ion irradiation-induced tetragonal distortion in Mn2CoAl Heusler films. The out-of-plane lattice constant continuously increases from 5.84 to 6.09 Å, while the in-plane lattice constant remains nearly unchanged. Magnetic measurements show that saturation magnetization at 50 K decreases from 258 emu/cc to 167 emu/cc under Ar ion irradiation. Transport measurements show that the longitudinal resistivity decreases with increasing irradiation doses, and the anomalous Hall resistivity changes from negative to positive. Moreover, it is found that hump-like anomalies can be observed in the Hall resistivity loops at the irradiation dose of 1×〖10〗^14 and 1×〖10〗^15 /cm2, which are attributed to the irradiation-induced inhomogeneous magnetism in the surface and interface parts. This work demonstrates the considerable tunability of the structure, magnetism and transport properties of Mn2CoAl Heusler alloys by Ar ion irradiation.

Crystal Structure and Properties of Heusler Alloys: A Comprehensive Review

“…For tetragonal X 3 Z (Z = Al, Ga, In Tl, Si, Ge, Sn, Pb) alloys, the X(A), X(B), X(C) and Z atoms occupy the (0, 0, 0), (0.25, 0.25, 0.25), (0.5, 0.5, 0.5) and (0.75, 0.75, 0.75) Wyckoff positions, respectively [22]. Thus, Chen et al [51] detected meta-stable tetragonal phase formation in Mn 2 CoAl upon Ar+ irradiation. They found that the saturation magnetization decreased, and an anomalous Hall resistivity progressively deviation from negative to positive was observed as a result of the structural deterioration.…”

Defect Engineering Of Perpendicular Magnetic Anisotropy In Cobalt-Based Thin Films

“…Gaier studied He + and Ga + irradiation effects on several Co based Heusler-alloy thin films [191]. Chen P. et al investigated changes in the structural and magnetic properties of 27 nm Mn2CoAl thin films irradiated with 30 keV Ar + ions, observing an increase in lattice constant, a decrease in saturation magnetization, and changes in Hall resistance [192]. Additionally, I. Abdallah et al explored the effects of 150 keV He + irradiation on 40 nm Co2MnSi thin films as a substitute for annealing to induce B2 order, noting a reduction in magnetization with increasing fluence, and later, they reported structural effects as well [193]- [195].…”