Coexistence of ferro- and antiferromagnetic order in Mn-doped Ni$_2$MnGa

TL;DR

This study investigates the magnetic ordering in Mn-doped Ni-Mn-Ga alloys, revealing the coexistence of ferro- and antiferromagnetic phases and how Mn content influences magnetization and structural stability.

Contribution

It combines experimental magnetization measurements with first-principles calculations to elucidate the magnetic interactions and phase stabilization in Mn-rich Ni-Mn-Ga alloys.

Findings

Magnetization peaks near stoichiometric composition and decreases with more Mn.

Extra Mn atoms are antiferromagnetically aligned, affecting overall magnetization.

Mn doping influences structural phase stability and magnetic anisotropy.

Abstract

Ni-Mn-Ga is interesting as a prototype of a magnetic shape-memory alloy showing large magnetic field induced strains. We present here results for the magnetic ordering of Mn-rich Ni-Mn-Ga alloys based on both experiments and theory. Experimental trends for the composition dependence of the magnetization are measured by a vibrating sample magnetometer (VSM) in magnetic fields of up to several tesla and at low temperatures. The saturation magnetization has a maximum near the stoichiometric composition and it decreases with increasing Mn content. This unexpected behaviour is interpreted via first-principles calculations within the density-functional theory. We show that extra Mn atoms are antiferromagnetically aligned to the other moments, which explains the dependence of the magnetization on composition. In addition, the effect of Mn doping on the stabilization of the structural phases and on the magnetic anisotropy energy is demonstrated.