Electronic structure study of the magnetoresistance materialCaCu3Mn4O12by LSDA andLSDA+U

Abstract

The electronic structure of the large low-field magnetoresistance material ${\mathrm{CaCu}}_{3}{\mathrm{Mn}}_{4}{\mathrm{O}}_{12}$ is calculated by using the local-spin-density approximation (LSDA) and on-site Coulomb interaction correction $(\mathrm{LSDA}+\mathrm{U})$ to the $3d$ electronic states of Cu and Mn ions. The results obtained suggest a strong ionic character of this material despite a presence of a partial Mn-O covalence effect. Three Cu ions per formula cell have their respective half-filled orbitals ${d}_{\mathrm{xy}},{d}_{\mathrm{yz}},$ and ${d}_{\mathrm{xz}}$ due to their different local crystal environments. Four Mn ions per formula cell have nearly the same oxygen coordinations. As a consequence, the spin-up ${t}_{2g}$-like orbitals ${(d}_{\mathrm{xy}}{,d}_{\mathrm{yz}},$ and ${d}_{\mathrm{xz}})$ are almost full-filled, while the spin-up ${e}_{g}$-like orbitals ${(d}_{{3z}^{2}\ensuremath{-}{r}^{2}}$ and ${d}_{{x}^{2}\ensuremath{-}{y}^{2}})$ are partially occupied due to a finite $\mathrm{pd}$ hybridization. And it is shown that the sublattices of Cu ions and Mn ones are both aligned in ferromagnetic order, while these two sublattices are coupled antiferromagnetically, thus giving a net spin moment of 9 ${\ensuremath{\mu}}_{B}$ per formula. The $\mathrm{LSDA}+\mathrm{U}$ calculation yields a semiconducting solution, which is improved upon a half-metallic state given by the LSDA calculation and consistent with an experimental measurement.