Two-step magnetic ordering into a canted state in ferrimagnetic monoclinic Mn$_3$As$_2$

TL;DR

This study reveals the temperature-dependent magnetic structures of monoclinic Mn$_3$As$_2$, showing a transition from ferrimagnetic to a canted non-collinear state, providing insights into magnetic ordering mechanisms in Mn-As compounds.

Contribution

The paper presents the first detailed neutron diffraction analysis of Mn$_3$As$_2$'s magnetic phases at different temperatures, uncovering a two-step magnetic transition and complex magnetic structures.

Findings

At 270 K, Mn$_3$As$_2$ exhibits ferrimagnetic order with Mn moments along $b$.

Below 225 K, Mn moments cant in the $ac$ plane, forming a multi-$k$ non-collinear structure.

The magnetic ground state changes with temperature, revealing factors influencing magnetic ordering in Mn-As compounds.

Abstract

We report the magnetic structure of room-temperature-stable, monoclinic Mn$_3$As$_2$ at 3 K and 250 K using neutron powder diffraction measurements. From magnetometry data, the Curie temperature of Mn$_3$As$_2$ was confirmed to be around 270 K. Calorimetry analysis showed the presence of another transition at 225 K. At 270 K, Mn$_3$As$_2$ undergoes a $k = 0$ ferrimagnetic ordering in the magnetic space group $C2/m$ (#12.58) with Mn moments pointing along $b$. Below 225 K, there is a canting of Mn moments in the $ac$ plane which produces a multi-$k$ non-collinear magnetic structure in space group $C2/c$ (#15.85). The components of Mn moments along $b$ follow $k=0$ ordering and the components along $a$ and $c$ have $k = [0 0 \frac{1}{2}]$ propagation vector. The change in the magnetic ground state with temperature provides a deeper insight into the factors that govern magnetic ordering in Mn-As compounds.