Room-temperature ferromagnetism in ${\mathrm{Sr}}_{1-x}{\mathrm{Y}}_x\mathrm{Co}{\mathrm{O}}_{3-\delta }$ $(0.2⩽x⩽0.25)$

We have measured magnetic susceptibility and resistivity of ${\mathrm{Sr}}_{1-x}{\mathrm{Y}}_x\mathrm{Co}{\mathrm{O}}_{3-\delta }$ ($x=0.1$, 0.15, 0.2, 0.215, 0.225, 0.25, 0.3, and 0.4), and found that ${\mathrm{Sr}}_{1-x}{\mathrm{Y}}_x\mathrm{Co}{\mathrm{O}}_{3-\delta }$ is a room temperature ferromagnet with a Curie temperature of $335\mathrm{K}$ in a narrow compositional range of $0.2⩽x⩽0.25$. This is the highest transition temperature among perovskite Co oxides. The saturation magnetization for $x=0.225$ is $0.25{\mu }_B∕\mathrm{Co}$ at $10\mathrm{K}$, which implies that the observed ferromagnetism is a bulk effect. We attribute this ferromagnetism to a peculiar $\mathrm{Sr}∕\mathrm{Y}$ ordering.

Figure 1

(a) Magnetization vs temperature $\left[M\left(T\right)\right]$ of ${\mathrm{Sr}}_{1-x}{\mathrm{Y}}_x\mathrm{Co}{\mathrm{O}}_{3-\delta }$ ($x=0.1$, 0.15, 0.2, 0.215, 0.225, 0.25, 0.3, and 0.4); (b) magnetization vs magnetic field $\left[M\left(H\right)\right]$ of ${\mathrm{Sr}}_{0.775}{\mathrm{Y}}_{0.225}\mathrm{Co}{\mathrm{O}}_{3-\delta }$. The insets of (a) and (b) show $M\left(T\right)$ and $M\left(H\right)$ of ${\mathrm{Sr}}_{0.775}{\mathrm{Y}}_{0.225}\mathrm{Co}{\mathrm{O}}_3$, respectively.

Figure 2

X-ray diffraction patterns of (a) ${\mathrm{Sr}}_{0.775}{\mathrm{Y}}_{0.225}\mathrm{Co}{\mathrm{O}}_{3-\delta }$ and (b) ${\mathrm{Sr}}_{0.775}{\mathrm{Er}}_{0.225}\mathrm{Co}{\mathrm{O}}_{3-\delta }$; (c) x-ray diffraction patterns around 26° of ${\mathrm{Sr}}_{1-x}{\mathrm{Y}}_x\mathrm{Co}{\mathrm{O}}_{3-\delta }$ ($x=0.1$, 0.15, 0.2, 0.225, 0.3, and 0.4) and ${\mathrm{Sr}}_{0.775}{\mathrm{Er}}_{0.225}\mathrm{Co}{\mathrm{O}}_{3-\delta }$.

Figure 3

Magnetization vs temperature of ${\mathrm{Sr}}_{0.775}{R}_{0.225}\mathrm{Co}{\mathrm{O}}_{3-\delta }$ ($R=\mathrm{Y},\mathrm{Dy}$, Ho, and Er). The inset shows $1∕M$ of ${\mathrm{Sr}}_{0.775}{\mathrm{Y}}_{0.225}\mathrm{Co}{\mathrm{O}}_{3-\delta }$.

Figure 4

Resistivity of ${\mathrm{Sr}}_{1-x}{\mathrm{Y}}_x\mathrm{Co}{\mathrm{O}}_{3-\delta }$ ($x=0.1$, 0.15, 0.2, 0.225, 0.25, 0.3, and 0.4). The arrow indicates the kink temperature in the inset of Fig. 3. The inset shows the resistivity of ${\mathrm{Sr}}_{0.775}{\mathrm{Y}}_{0.225}\mathrm{Co}{\mathrm{O}}_3$. The arrow indicates the Curie temperature.