Density functional theory studies of spin, charge, and orbital ordering in YBaT(2)O(5) (T = Mn, Fe, Co)

作者：Vidya R^*; Ravindran P; Knizek K; Kjekshus A; Fjellvag H

来源：Inorganic Chemistry, 2008, 47(15): 6608-6620.

DOI：10.1021/ic702025c

Spin, charge, and orbital orderings are influenced by electron/hole doping, cation radii, oxygen stoichiometry, temperature, magnetic field, and so on. In order to understand the role of electron/hole doping, we have studied variations in spin, charge, and orbital ordering in terms of d-band filling for YBaT(2)O(5) (T = Mn, Fe, Co). The calculations were performed using density functional theory as implemented in the full-potential linearized augmented-plane-wave method. We have carried out calculations for nonmagnetic, ferromagnetic, and antiferromagnetic configurations. A ferrimagnetic ground state was established for YBaMn(2)O(5), whereas YBaFe(2)O(5) and YBaCo(2)O(5) have antiferromagnetic ground states; all of these results are in agreement with experimental findings. The effects of spin-orbit coupling, the Hubbard U parameter, and orbital polarization on the magnetic properties were also analyzed. The electronic band characteristics were analyzed using total as well as site- and orbital-projected densities of states. Inclusion of spin-orbit coupling and Coulomb correlation effects in the calculations was found to be important in order to reproduce the experimentally established semiconducting behaviors of YBaFe(2)O(5) and YBaCo(2)O(5). In order to quantify the charges at each atomic site, we made use of the Bader "atom-in-molecule" concept and Born effective-charge (BEC) analyses. The structural optimizations and BEC tensor calculations were performed using the VASP-PAW method. The different types of charge and orbital orderings in these compounds were visualized using the energy-projected density matrices of the d electrons. Substantial differences in ordering patterns with respect to d-band filling emerged. Ordering of the d(z2) orbital of Mn in YBaMn(2)O(5) gave rise to G-type ferrimagnetic spin ordering along the c direction and checkerboard-type charge ordering, whereas ordering of the d(x2-y2) orbital of Fe in YBaFe(2)O(5) caused Wollan-Koehler G-type antiferromagnetic spin ordering along the b direction and stripe-type charge ordering. Similarly, a complex pattern of orbital ordering in YBaCo(2)O(5) activated spin and charge orderings similar to those in YBaFe(2)O(5).

• 出版日期2008-8-4