Orbital structure and magnetic ordering in stoichiometric and doped crednerite CuMnO 2

Abstract

The exchange interactions and magnetic structure in layered system CuMnO2 (mineral crednerite) and in nonstoichiometric system Cu1.04Mn0.96O2, with triangular layers distorted due to orbital ordering of the Mn3+ ions, are studied by ab initio band-structure calculations, which were performed within the GGA + U approximation. The exchange interaction parameters for the Heisenberg model within the Mn planes and between the Mn planes are estimated. We explain the observed in-plane magnetic structure by the dominant mechanism of the direct d-d exchange between neighboring Mn ions. The superexchange via O ions, with 90â̂̃ Mn-O-Mn bonds, plays a less important role for the in-plane exchange. The interlayer coupling is largely dominated by one exchange path between the half-filled 3z2-r2 orbitals of Mn3+. The change of interlayer coupling from antiferromagnetic in pure CuMnO2 to ferromagnetic in doped material is also explained by our calculations. © 2014 American Physical Society.