Field-induced spin-state transition in the perovskite cobalt oxide ${\text{Sr}}_{1-x}{\text{Y}}_x{\text{CoO}}_{3-\delta }$

High field magnetization and high-frequency electron spin resonance measurements on the perovskite Co oxide ${\text{Sr}}_{1-x}{\text{Y}}_x{\text{CoO}}_{3-\delta }$ ($x=0.22$ 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.

Figure 1

Temperature dependence of the magnetization in ${\text{Sr}}_{1-x}{\text{Y}}_x{\text{CoO}}_{3-\delta }$ with $x=0.22$ and 0.25, observed in the magnetic field of 0.1 T.

Figure 2

Frequency-field relation of the ESR resonance points in ${\text{Sr}}_{1-x}{\text{Y}}_x{\text{CoO}}_{3-\delta }$ with $x=0.22$ and 0.25, observed at 4.2 K. A solid line shows theoretical ferromagnetic resonance mode. The inset shows ESR spectra observed at 4.2 K.

Figure 3

Magnetization curves of ${\text{Sr}}_{1-x}{\text{Y}}_x{\text{CoO}}_{3-\delta }$ with $x=0.22$ and 0.25, observed at 4.2 K.

Figure 4

(a) Temperature dependence of the magnetization curves of ${\text{Sr}}_{1-x}{\text{Y}}_x{\text{CoO}}_{3-\delta }$ with $x=0.25$. Each magnetization curve shifts up by $0.05{\mu }_{\text{B}}$ with increasing temperature from 4.2 K. (b) Temperature dependence of the derivative of the magnetization $\left(dM/dH\right)$ curve of ${\text{Sr}}_{1-x}{\text{Y}}_x{\text{CoO}}_{3-\delta }$ with $x=0.25$ in the field-ascending process.

Figure 5

(a) Temperature dependence of the $H_{\text{c}}$, observed in ${\text{Sr}}_{1-x}{\text{Y}}_x{\text{CoO}}_{3-\delta }$ with $x=0.25$. Closed circles show the $H_{\text{c}}$. Open circles show the peak temperature $T_{\text{m}}$ of the $M-T$ curves, measured at $H=0.1$, 3, and 7 T. Solid curve shows a theoretical curve, calculated with the parameter, $g=3.6$, $\Delta =575\text{K}$, and $H_{\text{i}}=200\text{T}$. Dashed curve is that with the parameter, $g=3.6$, $\Delta =91\text{K}$, and no internal field.