Spin-state Transition Associated with the Magnetization Jump on Y$_{1-x}$Sr$_{x}$CoO$_{3-\delta}$ Compounds (x=0.67, 0.75)

Perovskite-type compounds Y$_{1-x}$Sr$_{x}$CoO$_{3}$ (x=0.67, 0.75) were prepared by the conventional solid state method and sintered under air and O$_{2}$ flow. There is a DC magnetization jump during the field cooling at 0.01 T and then it comes normally back to high temperature in the specimens, which is called as magnetic memory effect. The Co$^{3+}$ ions spin state transition from low to intermediate state results in the magnetization jump. The jump temperature ($T_{J})$ and magnetization increase with the x increases. With increasing the magnetic field, the magnetization jump disappears. Air-processed samples exhibit higher $T_{J}$ and larger magnetization than O$_{2}$-processed samples. The main reason is the different content of Co$^{3+}$ ions due to the oxygen deficiency under the different prepared conditions. Samples with x=0.75 show the higher Curie temperature ($T_{C})$ and at almost the same temperature the cusp appears in the zero-field curve. At the same time, there is another small cusp in the zero-field curve in x = 0.75 samples.