Orbital Delocalization and Enhancement of Magnetic Interactions in Perovskite Oxyhydrides

Recent experiments showed that some perovskite oxyhydrides have surprisingly high magnetic-transition temperature. In order to unveil the origin of this interesting phenomenon, we investigate the magnetism in SrCrO$_{\mathrm{2}}$H and SrVO$_{\mathrm{2}}$H on the basis of first-principles calculations and Monte Carlo simulations. Our work indicates that the Cr-O-Cr superexchange interaction in SrCrO$_{\mathrm{2}}$H is unexpectedly strong. Different from the previous explanation in terms of the H$^{\mathrm{-}}$ ion substitution induced increase of the Cr-O-Cr bond angle, we reveal instead that this is mainly because the 3$d$ orbitals in perovskite oxyhydrides becomes more delocalized since H$^{\mathrm{-}}$ ions have weaker electronegativity and less electrons than O$^{\mathrm{2-}}$ ions. The delocalized 3$d$ orbitals result in stronger Cr-O interactions and enhance the magnetic-transition temperature. This novel mechanism is also applicable to the case of SrVO$_{\mathrm{2}}$H. Furthermore, we predict that SrFeO$_{\mathrm{2}}$H will have unprecedented high Neel temperature because of the extraordinarily strong Fe-H-Fe $\sigma $-type interactions. Our work suggests the anion substitution can be used to effectively manipulate the magnetic properties of perovskite compounds.