Structural, electronic and magnetic properties of TlFeSe₂ under high pressure

Abstract

The high-pressure (HP) properties of TlFeSe 2 are investigated based on the first-principles calculations combined with structure-searching method. The low-pressure C2/m phase will transform into the orthorhombic Pnma phase at 2 GPa, with 8% volume collapse, the insulator-metal transition and the bicollinear antiferromagnetic-to-nonmagnetic spin-crossover. At pressure higher than 8 GPa, the HP C2/m phase will become the ground state. Both Pnma phase and HP C2/m phase are constituted by one-dimensional chains of edge-sharing FeSe 5 tetragonal pyramids. Pressuring decrease the Se-Se bond length giving rise to the transition from [Se 2 ] 3− to [Se 2 ] 2− . Negative charge transfer causes the Fe 2+ with ∼2 μ B magnetic moment at ambient pressure and the nonmagnetic Fe 1.5+ at higher pressure. The Fermi surfaces of HP phases are also discussed.