Mechanisms of the insulator–metal transition and spin crossover in CoO at high pressure

The effect of high pressure on the electronic characteristics of CoO is analyzed in the framework of the multielectron model of transition metal oxides. The specific features of spin crossover for $d^7$ terms of Co$^{+2}$ are compared to those characteristic of $d^5$ and $d^6$ configurations. A pressure-induced transition between antiferromagnetic and ferromagnetic states at the spin crossover point is predicted. A model is proposed to describe the pressure-induced variation of the electrical resistance exhibiting a stepwise change by eight orders of magnitude at the structural transition point observed at 43 GPa and the subsequent metallization above 133 GPa.