Positron-annihilation study of the half-metallic ferromagnet NiMnSb: Experiment.

Abstract

Spin-polarized measurements of the two-dimensional angular correlation of annihilation radiation in NiMnSb are presented. By making use of the inherent partial polarization of the positron beam and the alignment of the magnetic domains with the aid of an external magnetic field, the sum and difference of the spin-dependent contributions to the angular correlation have been obtained for integration directions 〈100〉, 〈110〉, and 〈111〉. The results are compared with calculated distributions. A least-squares analysis of the data yields a value of (-8.4\ifmmode\pm\else\textpm\fi{}0.1)\ifmmode\times\else\texttimes\fi{}${10}^{\mathrm{\ensuremath{-}}3}$ for the three-photon difference effect in NiMnSb and establishes the half-metallic character of the band structure with an accuracy of ${\mathrm{\ensuremath{\sim}}}_{\mathrm{\ensuremath{-}}0.02}^{+0.01}$ electrons per formula unit.