First-principles study of electronic and magnetic structure in layered cobaltite Na_(0.75)CoO_(2)

摘要

The electronic structure of Na_(0.75)CoO_(2) has been calculated by the LDA+U method, considering the location of Na ions. The magnetic moments of Co ions are strongly influenced by the bond distances between the Co and Na ions, and are unusually distributed. This implies the occurrence of a charge disproportionation state (2Co~(3.25+)→Co~(3.25+δ)+Co~(3.25-δ)) in this material. The magnetic ground state of Na_(0.75)CoO_(2) is therefore a spin-glass-like, short-range ordered state resulting from randomly distributed magnetic Co ions.