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

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+?, La2CoO4, 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 NaxCoO2 ? yH2O ? are also given significant attention.