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

Abstract Tetragonal Heusler alloys have attracted increasing interest due to their great scientific and technological applications 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 (OOP) distortion of cubic Heusler alloys. In this work, we report the ion irradiation-induced tetragonal distortion in Mn 2 CoAl Heusler films. The OOP 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 −1 to 167 emu cc −1 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 cm −2 , 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 Mn 2 CoAl Heusler alloys by Ar ion irradiation.