Band topology resisted spin-state evolution of perovskite ACoO[formula omitted] (A = Ca, Sr) under pressure

Abstract

There has been a debate on the theoretical explaining of the spin states in the perovskite ACoO3, especially SrCoO3. The aim of this work was to investigate the magnetic phase stability and to study the evolution of the spin states of the cubic perovskite ACoO3 (A = Ca, Sr) under pressure up to 40 GPa by using the density functional theory and the Hubbard +U parameters (DFT+U). Both CaCoO3 and SrCoO3 exhibit the ferromagnetic and metallic properties under pressure. Our results of the total magnetization and the net-spin density corroborate that a change of the magnetic behaviors on ACoO3 mostly depends on the value of Co-O bond length (dCo−O). We discovered a down-stepwise evolution of the total magnetization as a relationship with the dCo−O decreasing. This stepwise behavior occurs prior to the spin crossover from intermediate spin (IS) state to low spin (LS) state. The total magnetization values non-monotonically decreased from 2.49 to 2.16 μB/f.u. between the dCo−O = 1.88 and 1.80 Å. From our evidence, we indicated that the spin state of Co-3d states resembles the d7L̲2 character with t2g3↑,2↓eg2−x↑,x↓L̲2 state, where x≈0.5 and L̲ denotes the oxygen’s charge transfer from the oxygen ligands. Indeed, we discovered that the stepwise evolution of the total magnetization is associated with the changes in the band topology of the Co-3deg∗ band.