The spin-state transition in ACo2O4 spinels (A = Be, Mg, Ca, Cd, Zn)

Abstract

The magnetic and electronic properties of the Co-based spinel oxides ACo2O4 (A = Be, Mg, Ca, Zn, Cd) were studied within GGA + U approach. It was found that the Co3+ ion is in a low-spin state due to the effect of the crystal field of octahedral symmetry. It is shown that Co3+ ion undergoes a spin-state transition into the high-spin state under the critical pressure of P = −10 GPa – −20 GPa. This pressure-induced spin-state transition is caused by the redistribution of electrons between the t2g- and eg-orbitals arising with increasing interatomic distances. The role of interatomic distances between Co3+ ion and its ligands is discussed. Thin-film form also favors the appearance of a high-spin state of Co3+ ion. At the same critical pressure, there is a sharp increase in the majority spin bandgap and a sharp decrease in the minority spin bandgap. These findings allow manipulating the spin state of Co3+ ions and bandgap width through the pressure or strain arising in thin films.