Ab initio study of CrNF: the first half-metallic ferromagnet nitride fluoride mimicking CrO2

Abstract

Based on the different covalent versus ionic chemical bonding and isoelectronic rutile CrO2, CrNF is proposed starting from ordered rutile derivative structures subjected to full geometry optimizations. The ground state structure defined from cohesive energies is of MgUO4-type, characterized by short covalent Cr-N and long ionic Cr-F distances. Like CrO2 it is a half-metallic ferromagnet with M = 2 Bohr Magnetons integer magnetization per formula unit with reduced band gap at minority spins. Major differences of magnetic response to pressure characterize CrNF as a soft ferromagnet versus hard magnetic CrO2. The chemical bonding properties point to prevailing covalent Cr-N versus ionic Cr-F bonding. Synthesis routes with two different protocols are proposed and analyzed.