Cu ⁺ ‐Driven Ferroionic Structure and Pressure‐Tunable Magnetism in Layered Thiophosphate CuVP ₂ S ₆

Abstract

ABSTRACT Two‐dimensional (2D) van der Waals (vdW) magnets offer a versatile platform to explore fundamental physics and low‐dimensional functionalities. Metal thiophosphates (MTPs) with mobile Cu + ions exhibit a ferroionic state, where polarization arises from ionic redistribution among multiple nearly degenerate sites. CuVP 2 S 6 uniquely combines intrinsic ferromagnetism from the V sublattice with Cu + ‐driven ferroionic configurational freedom, enabling direct exploration of how ionic dynamics influence magnetic interactions. Herein, high‐quality CuVP 2 S 6 single crystals are synthesized, and their structural and physical properties are systematically investigated. Temperature‐dependent neutron diffraction elucidates a ferroionic structure with dynamic distributions of copper ions across multiple crystallographic sites. The versatile occupations are driven by local symmetry‐controlled orbital interactions between copper ions and surrounding ligands through a second‐order Jahn–Teller mechanism. Magnetic measurements identify a ferromagnetic (FM) transition below 3.3 K. The pressure‐controlled magnetocrystalline anisotropy and interlayer exchange interactions mediated by Cu + migration are demonstrated, boosting the Curie temperature remarkably by over 60% and inducing a soft‐to‐hard FM transition unparalleled within the MTP family. These results demonstrate that ionic configurational freedom provides an efficient route to control magnetism, opening new possibilities for spintronic applications.