Spin crossovers in Mott–Hubbard insulators at high pressures

The high-pressure induced phase transitions initiated by electronic transition in 3d ions from the high-spin (HS) to the low-spin (LS) state (HS-LS spin-crossover) are considered. Behavior of the system with d6 electronic configuration is investigated in the ground state of zero temperature and critical pressure Pc. Magnetic properties of the Mott–Hubbard insulator (Mg1−xFex)O are studied in the vicinity of the quantum critical point (T=0, Pc). At the critical pressure of spin crossover Pc, the spin gap energy εS between HS and LS states is zero. The quantum spins fluctuations HS⇔LS do not require any energy, and the antiferromagnetism is destroyed in the quantum critical point by the first order transition.