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

By first principles simulation, we studied the magnetic properties of Ca6(Li0.5Fe0.5)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(Li0.5Fe0.5)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 μB, and the orbital moment is 0.15 μB, 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 μB to 1 μB 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.