Observation of magnetization jump associated with a spin-state transition in oxygen-deficient Y0.33Sr0.67CoO3-δ

dc magnetization, electronic transport, and structural properties are studied on the mixed valence rare earth Sr-doped cobaltites Y0.33Sr0.67CoO3-delta. Oxygen deficiency and alternative layered structure with CoO6 octahedron and CoO4 tetrahedral polyhedron lead to the mixed valence states of Co ions. We found a Curie temperature at 304 K and a magnetization jump around 200 K under 0.01 T with a thermal hysteresis indicating a kind of magnetic memory effect. Temperature dependence of the electrical resistance exhibits nonmetallic with a thermal activation type. The observed magnetization jump is interpreted in term of a spin state transition of Co3+ ions in the octahedral site from the intermediate to low spin state. The intermediate spin configuration of Co3+ with t(2g)(5)e(g)(1) may develop an orbital ordering which accounts for the nonmetallic transport. With increasing magnetic field, the magnetization jump gradually disappears and its onset temperature shifts to lower temperature. The oxygen rich compound Y0.33Sr0.67CoO2.704 with 6% rich Co3+ population compared to the less oxygen compound Y0.33Sr0.67CoO2.614 shows a relatively large magnetization jump as well as the enhancement of the e(g) electron localization leading to higher magnetic transition temperature from the intermediate to low spin state. Contrary, the less oxygen Y0.33Sr0.67CoO2.614 shows the substantial low oxidation state as Co2+ which guides to a possible intermediate spin state stabilization.