Magnetic moment and spin state transition on rare monovalent iron ion in nitridoferrate Ca6Li0.5Fe0.5Te2N3

Abstract

By first principles simulation, we studied the magnetic properties of Ca₆(Li_0.5Fe_0.5)Te₂N₃ including the spin moment, orbital moment, and pressure-driven spin state transition of Fe ion from the high-spin (S = 3/2) to the low-spin (S = 1/2) state. Our spin-polarized calculations have correctly revealed that Ca₆(Li_0.5Fe_0.5)Te₂N₃ is a magnetic semiconductor with a band gap of 0.49 eV. The spin moment around the Fe ion with a 3d⁷ configuration is 3.0 μ_B, and the orbital moment is 0.15 μ_B, which is contrary to the large orbital moment suggested by experiment. With increasing pressure, a high-spin to low-spin state transition with an Fe moment collapse from 3 μ_B to 1 μ_B occurs at 18 GPa, accompanied by a semiconductor to metal transition. The underlying mechanism is explained in terms of the interplay between the crystal field and the electron population of the Fe 3d orbitals.