The Role of Magnetism and Phonons in the Negative Thermal Expansion of Layered Chromium Telluride

Abstract

Unraveling the origin of negative thermal expansion (NTE) in magnetic solids remains an open challenge, often obscured by the complex entanglement of spin and lattice dynamics. Here, leveraging the layered architecture of nominally Cr0.95Te, we distinguish the magnetic and phononic contributions to its anomalous thermal expansion. Neutron powder diffraction identifies a canted ferromagnetic (CFM) state at low temperatures (10–140 K), wherein the ferromagnetic component contributes to the lattice contraction within the a-b plane. Beyond magnetic effects, the low-frequency anharmonic vibrations of Te atoms, characterized by large positive c-axis mode Grüneisen parameters, act as a thermodynamic driver for a colossal lattice expansion along the c-axis. Notably, mediated by the comparatively rigid Cr–Te linkages, this axial response also generates a transverse contractile tendency within the a-b plane. The resulting volumetric NTE (αv = −10.7 × 10–6 K–1, 250–350 K) therefore arises from a “geometric coupling” mechanism between phonons and magnetic ordering. These findings provide insight into anomalous thermal expansion in layered magnets.