Reduced surface magnetization of NiMnSb(001)

Abstract

The spin-dependent electronic structure at the (001) surface of the ferromagnetic half-Heusler alloy NiMnSb has been investigated by spin-resolved appearance potential spectroscopy. This surface-sensitive technique provides access to the spin- and element-resolved local density of unoccupied states and, therefore, probes the spin polarization above the Fermi level. In combination with low-energy electron diffraction and magneto-optical Kerr effect measurements, we characterized the sample with respect to its crystal structure, electronic structure, and magnetic properties. Our spectroscopic experiments were accompanied by a quantitative theoretical analysis. The theoretical appearance potential spectra are based on self-consistent electronic structure results for the bulk. They have been obtained in a fully relativistic framework as a self-convolution of the matrix element-weighted, orbitally resolved unoccupied density of states. The spin asymmetry in the experimental results, obtained from the surface region, is found to be significantly reduced compared with the calculations based on the bulk electronic structure of NiMnSb. Possible reasons for the reduced surface magnetization are discussed.