Ordered oxygen deficient �?112’ perovskites, LnBaCo2O5.50+�?: complex magnetism and transport properties

[摘要] The ordered oxygen deficient `112’ perovskites, LnBaCo₂O_{5.50+ð›�?} (Ln = lanthanide or Y), exhibit a very flexible structure which can either uptake (ð›�? > 0) or release oxygen (ð›�? < 0) depending on the experimental conditions of synthesis and on the size of the lanthanide. These compounds exhibit remarkably complex magnetic transitions, metalâ€�?�insulator transition and exceptionally high magnetoresistance. We show herein that their physics is mainly dominated by three different ferromagnetic states, depending on the cobalt valency: FM1 for ð›�? = 0 (Co³⁺), FM2 for ð›�? < 0 (Co²⁺/Co³⁺) and FM3 for ð›�? > 0 (Co³⁺/Co⁴⁺). The competition between ferromagnetism and antiferromagnetism in these phases and the various transitions are discussed taking into consideration the spin state of cobalt, the issue of phase separation and the effect of cobalt coordination and disproportionation.

[学科分类] 材料工程

[关键词] Ordered oxygen deficient perovskites;`112’ cobaltites;ferromagnetic cobaltites;phase separation;magnetic transitions;magnetoresistive cobaltites.