Pressure-Induced Chemical Bonding Effects on Lattice and Magnetic Instabilities in Antiferromagnetic Insulating CaMn$_2$Sb$_2$

TL;DR

This study investigates how applying pressure induces structural, electronic, and magnetic phase transitions in CaMn₂Sb₂, revealing a complex interplay of charge localization, orbital reconfiguration, and magnetic order changes.

Contribution

It provides detailed insights into pressure-driven phase transitions and magnetic order evolution in CaMn₂Sb₂, highlighting the coupling between structural distortion, charge redistribution, and magnetism.

Findings

First-order phase transition at 5.4 GPa with volume collapse

Charge localization along Mn-Sb chains before transition

Pressure-induced incommensurate magnetic order

Abstract

Exotic quantum phenomena often emerge near an electronic delocalization transition (EDT) from an antiferromagnetic insulating phase to a strongly correlated metallic state under pressure. We report the pressure-induced structural and magnetic evolution of the antiferromagnetic insulator CaMn$_2$Sb$_2$. Single-crystal X-ray diffraction reveals a first-order phase transition near 5.4 GPa from a trigonal P-3m1 structure to a monoclinic P2$_1$/m phase, accompanied by a ~7% volume collapse. Residual electron density analysis at intermediate pressures reveals charge localization along Mn-Sb chains, signaling electronic instability preceding the structural transition. Bonding analysis indicates anisotropic Mn-Sb orbital reconfiguration under pressure, driving a distorted square-pyramidal geometry. Neutron scattering confirms the transition and identifies a pressure-induced incommensurate magnetic order, distinct from the ambient antiferromagnetic state. In the monoclinic phase, zigzag Mn chains exhibit antiferromagnetic coupling along the ac-plane, enabled by enhanced orbital overlap. These results establish CaMn$_2$Sb$_2$ as a model system for studying the coupling of structural distortion, charge redistribution, and magnetic order in layered Mn pnictides under pressure.