Pressure-Stabilized MnSb$_2$ with Complex Incommensurate Magnetic Order

TL;DR

This study reports the stabilization and detailed magnetic characterization of MnSb$_2$, a metastable marcasite-type compound under high pressure, revealing complex, temperature-dependent magnetic order with potential for unconventional magnetic phenomena.

Contribution

First demonstration of pressure stabilization of MnSb$_2$ and comprehensive analysis of its complex magnetic ground state using neutron diffraction.

Findings

MnSb$_2$ is stable at ambient conditions up to 450-500 K.

Magnetic order is complex and temperature-dependent, with a propagation vector changing with temperature.

The magnetic structure is predominantly collinear with minimal canting, and exhibits a tunable modulation.

Abstract

Marcasite-type compounds have been proposed as promising hosts of exotic magnetic quantum states, yet experimental realizations in stoichiometric, disorder-free systems remain limited. Here, we report the high-pressure stabilization and magnetic characterization of MnSb$_2$, a marcasite-type compound that is thermodynamically metastable under ambient pressure. Single crystals were synthesized using a cubic multi-anvil press, and powder and single-crystal X-ray diffraction confirm the orthorhombic $Pnnm$ structure. These crystals are stable at ambient pressure for a long time up to between 450-500 K. Heat-capacity measurements reveal phase transitions at approximately 220 K and 118 K. Neutron diffraction uncovers an unconventional magnetic ground state below 220 K. Magnetic powder neutron diffraction refinements reveal possible multiple magnetic configurations that provide comparably acceptable fits to the experimental data. While most solutions are consistent with a spin-density-wave (SDW) description, helical models systematically yield inferior agreement factors. Across a broad range of models, the Mn ordered moment reaches a maximum value of approximately 2 $\mu_B$ and remains predominantly collinear, with minimal canting along the $c$-axis. At 200 K, the magnetic propagation vector is $q$ = (0, 0.3975, 0.3783); upon cooling, the $b$ component increases toward 0.5, reflecting a temperature-dependent evolution of the modulation. The need for modification of the magnetic model between high and low temperatures further highlights the complex and strongly temperature-dependent nature of the magnetic order in this system. These results establish MnSb$_2$ as a pressure-stabilized marcasite magnet with a highly tunable, complex magnetic ground state and a compelling stoichiometric platform for exploring unconventional magnetic behavior, including potential altermagnetism.