Minority-spin band parameters in a NiMnSb thin film determined by spectral conductivity

Abstract

NiMnSb is expected to be a ferromagnetic half metal, an expectation that is based in part on band structure calculations. Here we report optical conductivity studies of the band structure for a film prepared by pulsed laser deposition onto a Si substrate held at a relatively low temperature as is required for some device applications - films which are susceptible to site disorder associated with the vacant site in this half-Heusler compound. We demonstrate that the direct interband transitions are essentially unshifted in comparison with bulk material, though they are somewhat broadened. Below the direct-transition absorption edge we report the presence of indirect spin-reversing transitions between the Fermi energy (Ef) and the extrema of the minority-spin valence and conduction bands, providing a measure of the band edge energies. Both of these edges appear closer to Ef than is seen in well-ordered bulk NiMnSb, with the conduction-band minimum showing weight at only 200 cm-1 above Ef, close enough to have substantial occupation at ambient temperature. © 2004 American Institute of Physics.