Specific features of spin, charge, and orbital ordering in cobaltites

Abstract

Complex cobalt oxides known as cobaltites are reviewed, including LnCoO3-based perovskite-structured rare-earth cobaltites (where Ln is lanthanum or a lanthanide), quasi-two-dimensional and quasi-one-dimensional cobaltites of the types LnCo2O5+δ, La 2CoO4, and Ca3Co2O8, and NaxCoO2 yH2O superconducting compounds. Key experimental and theoretical results are presented, with emphasis on the interplay between charge, spin, and orbital degrees of freedom. Two problems of specific relevance to cobaltites - the spin state instability of Co3+ ions in LnCoO3, and the nature of superconductivity in Na xCoO2 yH2O - are also given significant attention. © 2009 Uspekhi Fizicheskikh Russian Academy of Sciences.