Magnetoelectronic properties of a ferrimagnetic semiconductor: The hybrid cupromanganite CaCu3Mn4O12

The mixed manganite cuprate CaCu3Mn4O12 is calculated, using density functional methods, to be a spin-asymmetric ferrimagnetic semiconductor with a small gap, Cu (formally spin 1/2) antialigns with Mn (formally spin 3/2), and the net spin moment is 9mu(B), consistent with the formal spins. The valence-band maximum has Cu d(xy)-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.