Simultaneous metal–half-metal and spin transition in SrCoO3 under compression

Abstract

In experiments, strontium cobaltite (${\mathrm{SrCoO}}_{3}$) has been confirmed to be a ferromagnetic metal (Curie temperature ${T}_{C}\ensuremath{\approx}305\phantom{\rule{3.33333pt}{0ex}}\mathrm{K}$) at ambient conditions and remains in cubic perovskite structure up to $\ensuremath{\sim}60\phantom{\rule{3.33333pt}{0ex}}\mathrm{GPa}$. Using local density approximation + self-consistent Hubbard $U$ ($\mathrm{LDA}+{U}_{\mathrm{sc}}$) calculations, we show that ferromagnetic metallic ${\mathrm{SrCoO}}_{3}$ at low pressure is in an intermediate-spin (IS) state with ${d}^{6}\underline{L}$ character: nearly trivalent (${\mathrm{Co}}^{3+}$) instead of tetravalent cobalt (${\mathrm{Co}}^{4+}$) accompanied by spin-down O-$2p$ electron holes (ligand holes $\underline{L}$). Our calculations further predict that upon compression ($\ensuremath{\gtrsim}7\phantom{\rule{3.33333pt}{0ex}}\mathrm{GPa}$), ${\mathrm{SrCoO}}_{3}$ undergoes a transition to a low-spin (LS) ferromagnetic half-metal with an energy gap opened in the spin-up channel. Compared to the metallic IS state, the half-metallic LS state exhibits even more prominent ${d}^{6}\underline{L}$ character, including nearly nonmagnetic ${\mathrm{Co}}^{3+}$ and exceptionally large oxygen magnetic moments, which contribute most of the magnetization. By analyzing x-ray diffraction data of compressed single-crystal ${\mathrm{SrCoO}}_{3}$, we point out an anomalous volume reduction of $\ensuremath{\sim}1$%. This previously unnoticed volume anomaly is in great agreement with our predictive calculations, providing quantitative evidence for the simultaneous metal--half-metal and spin transition in ${\mathrm{SrCoO}}_{3}$.