Magnetoelectronic properties of a ferrimagnetic semiconductor: The hybrid cupromanganiteCaCu3Mn4O12

The mixed manganite cuprate ${\mathrm{CaCu}}_3{\mathrm{Mn}}_4{\mathrm{O}}_{12}$ is calculated, using density functional methods, to be a spin-asymmetric ferrimagnetic semiconductor with a small gap. Cu (formally spin $\frac{1}{2})$ antialigns with Mn (formally spin $\frac{3}{2}),$ and the net spin moment is $9{\mu }_B,$ consistent with the formal spins. The valence-band maximum has Cu $d_{\mathrm{xy}}–\mathrm{O}$ $p_{\sigma }$ character with spin aligned antiparallel with the net magnetization; the conduction-band minimum has the opposite spin and mixed Cu-Mn character. This spin-asymmetric gap (1) implies a thermally induced current that is 100% spin polarized and (2) leads to a field-induced narrowing of the energy gap. The relationship of these properties to the reported magnetoresistance is discussed.