Supercritical CO2-modulated phase transition in CaSnO3 from orthorhombic to cubic symmetry for room-temperature ferromagnetism

Abstract

The advancement of nanotechnology has enabled magnetic nanomaterials to exhibit remarkable potential and application value in medicine, transportation, information storage, and spintronics owing to their unique physicochemical properties. In this study, supercritical carbon dioxide (SC CO₂) was used to successfully induce room-temperature ferromagnetism in CaSnO₃ without magnetic element doping, achieving a maximum saturation magnetization of 0.0727 emu g⁻¹ at 16 MPa. The SC CO₂ treatment introduced lattice-scale defects, releasing residual force within distorted SnO₆ octahedra, which led to the suppression of structural distortion and drove a structural phase transition from orthorhombic to cubic. Additionally, the enhanced symmetry was accompanied by anisotropic lattice expansion and tensile strain, which thermodynamically lowered the oxygen vacancy formation energy, thereby kinetically driving the creation of more defects. This disrupted the intrinsic antiferromagnetic order and significantly enhanced ferromagnetism. This work elucidates a defect-strain synergy mechanism for tuning material magnetic order, distinguishing it from conventional stoichiometric doping strategies and highlighting the critical role of SC CO₂ in material modification.