Field-induced spin-state transition in the perovskite cobalt oxide Sr1-xYxCoO3-δ

High field magnetization and high-frequency electron spin resonance measurements on the perovskite Co oxide ${\text{Sr}}_{1\ensuremath{-}x}{\text{Y}}_{x}{\text{CoO}}_{3\ensuremath{-}\ensuremath{\delta}}$ ($x=0.22$ and 0.25) have been performed in magnetic fields up to 53 T. We have observed the spin-state transition, induced by the external magnetic fields, for the sample with $x=0.25$. A distinctive feature of this field-induced spin-state transition is that it is assisted by an internal field, originating from ferromagnetic exchange interaction between ${\text{Co}}^{3+}$ ions.