Canted Antiferromagnetism in Polar MnSiN$_2$ with High N\'eel Temperature

TL;DR

This study reveals canted antiferromagnetism in MnSiN$_2$, a high N{é}el temperature transition metal nitride, combining experimental and theoretical methods to elucidate its magnetic structure and underlying superexchange interactions.

Contribution

The paper provides the first detailed magnetic structure of MnSiN$_2$, demonstrating a high N{é}el temperature and a canted antiferromagnetic ground state supported by DFT and neutron diffraction.

Findings

N anions enhance superexchange leading to high T_N of 443 K

Magnetic structure includes a 10° spin rotation and 0.6° canting

Magnetic symmetry lowers to Pc' from G-type order

Abstract

MnSiN$_2$ is a transition metal nitride with Mn and Si ions displaying an ordered distribution on the cation sites of a distorted wurtzite-derived structure. The Mn$^{2+}$ ions reside on a 3D diamond-like covalent network with strong superexchange pathways. We simulate its electronic structure and find that the N anions in MnSiN$_2$ act as $\sigma$- and $\pi$-donors, which serve to enhance the N-mediated superexchange, leading to the high N\'{e}el ordering temperature of $T_N$ = 443 K. Polycrystalline samples of MnSiN$_2$ were prepared to reexamine the magnetic structure and resolve previously reported discrepancies. An additional magnetic canting transition is observed at $T_\mathrm{cant}$ = 433 K and the precise canted ground state magnetic structure has been resolved using a combination of DFT calculations and powder neutron diffraction. The calculations favor a $G$-type antiferromagnetic spin order with lowering to $Pc^\prime$. Irreducible representation analysis of the magnetic Bragg peaks supports the lowering of the magnetic symmetry. The computed model includes a 10$^\circ$ rotation of the magnetic spins away from the crystallographic $c$-axis consistent with measured powder neutron diffraction data modeling and a small canting of 0.6$^\circ$.