Various magnetic states for novel layered cobalt oxides CaCo6O11 and BaCo6O11

Abstract

Novel layered cobalt oxides ACo₆O₁₁ (A = Ca, Ba) have been synthesized under high-pressure and high-temperature conditions of 8 GPa and 1373 K, respectively. Both oxides crystallize in magnetoplumbite-related structures with hexagonal symmetry of the space group (P6₃/mmc, no. 194), as well as SrCo₆O₁₁. The magnetic ground state systematically transforms from antiferromagnetic-like (CaCo₆O₁₁) to ferrimagnetic (SrCo₆O₁₁) to ferromagnetic (BaCo₆O₁₁) by changing the A-site ion. These magnetic transitions are dominated by the superexchange interactions between magnetic CoO₅ trigonal bipyramids. Furthermore, CaCo₆O₁₁ exhibits a magnetic-field-driven phase transition from an antiferromagnetic-like to a ferrimagnetic state. Rietveld analysis indicates that the overall magnetic phase diagram for the ACo₆O₁₁ series provides a wide variety of electronic states induced by structure and the magnetic field.