Layer-resolved spin polarization in Sb overlayers on NiMnSb

The magnetism of antimony overlayers on a ferromagnetic substrate is invest igated by spin-polarized inverse photoemission and explained in terms of a spin-dependent envelope-function approximation (SDEFA). The atomic structur e of the films, which were deposited by sputtering Sb onto a NiMnSb(001) su bstrate, is characterized by a unique combination of three features: (i) Ni MnSb is a highly spin-polarized semi-Heusler alloy predicted to be halfmeta llic, (ii) antimony is a semimetal, exhibiting a band structure reminiscent of indirect-gap semiconductors, and (iii) the small lattice mismatch ensur es a well-controlled interface. Combined x-ray absorption spectroscopy and spin-polarized inverse photoemission yield a layer-resolved spin polarizati on decaying on a length scale of the order of 1 nm. The unusual range of th e spin polarization in the paramagnetic overlayer is explained by consideri ng the alloy-antimony interface as a spin-dependent perturbation potential and taking into account the low effective masses of the Sb conduction elect rons (only about 0.1 for both electrons and holes). (C) 2001 American Insti tute of Physics.