Magnetic properties and photoinduced magnetism on Y 0.25 Sr 0.75 CoO 3– δ

Magnetic properties and light‐induced magnetism on Y 0.25 Sr 0.75 CoO 3– δ under different sintered temperatures have been investigated. A magnetization jump around 179 K ( T J ) with a thermal hysteresis was found out in Y 0.25 Sr 0.75 CoO 2.688 sintered at 1250 °C. Whereas, there is a hysteresis at the onset of 145 K without magnetization jump appears in Y 0.25 Sr 0.75 CoO 2.626 sintered at 1100 °C together with the larger magnetization and lower Curie temperature. The large magnetization may come from the contribution of the surface/volume ferromagnetism in Co 3+ ions. A light‐induced spin‐state transition of Co 3+ ions from the nonmagnetic low‐spin state ( $ {\rm t}^{6}_{\rm 2g} {\rm e}^{0}_{\rm g} $ ); S = 0) to magnetic intermediate‐spin state ( $ {\rm t}^{5}_{\rm 2g} {\rm e}^{1}_{\rm g} $ ; S = 1) was observed in Y 0.25 Sr 0.75 CoO 2.688 , which increases the magnetization below T J . (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)