Structure and magnetic properties on Y$_{0.26}$Sr$_{0.72}$CoO$_{3-\delta }$ single crystal

We studied structural and magnetic properties on a single crystal of Y$_{0.33}$Sr$_{0.67}$CoO$_{3-\delta}$ in nominal composition. Single crystal was grown by the floating-zone method with radiation heating. Both electron-probe microanalysis (EPMA) and inductively coupled plasma (ICP) spectroscopy indicated the obtained single crystal was Y$_{0.26}$Sr$_{0.72}$CoO$_{3-\delta}$ in composition. The iodometric titration gives the oxygen content of 2.95. These results show that almost all Co ions are in trivalent state. The dc magnetization increases remarkably to reach a maximum at 301 K, then falls abruptly with decreasing temperature after both cooling and zero-field cooling. These behaviors were interpreted as a successive transition in which with decreasing temperature there is a transition from paramagnetic to ferromagnetic and eventually the antiferromagnetic properties appear at low temperatures. This should be associated with a successive spin state transition of Co ions [1, 2]. The detailed structural study and magnetic anisotropy will be reported and discussed with respect to a possible spin state change of Co ions. [1] Y. F. Zhang et al., accepted by Phys Rev. B for publication. [2] Y. F. Zhang et al., published in JMMM.