On the rich magnetic phase diagram of (Ni, Co)-Mn-Sn Heusler alloys

TL;DR

This study uses first principles simulations to explore the complex magnetic phase diagram of (Ni,Co)-Mn-Sn Heusler alloys, revealing multiple ferrimagnetic states, reduced magneto-volume coupling, and a tetragonal ground state with intricate spin arrangements.

Contribution

It uncovers a rich magnetic landscape with numerous local minima and identifies a previously overlooked tetragonal ground state in (Ni,Co)-Mn-Sn alloys.

Findings

Multiple ferrimagnetic states with similar energies and magnetizations.

Reduced magneto-volume coupling due to Ni, Co, and Sn atoms.

Tetragonal ground state with complex spin structure and zero magnetization.

Abstract

We put a spotlight on the exceptional magnetic properties of the metamagnetic Heusler alloy (Ni,Co)-Mn-Sn by means of first principles simulations. In the energy landscape we find a multitude of local minima, which belong to different ferrimagnetic states and are close in total magnetization and energy. All these magnetic states correspond to the local high spin state of the Mn atoms with different spin alignments and are related to the magnetic properties of Mn. Compared to pure Mn, the magneto-volume coupling is reduced by Ni, Co, and Sn atoms in the lattice and no local low-spin Mn states appear. For the cubic phase we find a ferromagnetic ground state whereas the global energy minimum is a tetragonal state with complicated spin structure and vanishing magnetization which so far has been overlooked in simulations.