Density of States of Ni: Soft-X-Ray Spectrum and Comparison with Photoemission and Ion Neutralization Studies

Abstract

Soft-x-ray studies have been made on paramagnetic Ni and interpreted in terms of the single-particle density of states. In particular, the ${M}_{2,3}$ emission spectrum has been investigated, using improved experimental techniques. Measurements were made at 960\ifmmode^\circ\else\textdegree\fi{}C, at an average pressure of 5\ifmmode\times\else\texttimes\fi{}${10}^{\ensuremath{-}8}$ Torr, using an oxide-free surface. Fine structure was observed in the spectrum. Although first-principles correction of self-absorption effects and satellite and subband overlap is not yet possible, careful consideration is given them, with the result that the ${M}_{3}$ band can be resolved from the accompanying structure in a plausible way. Most of its features can be taken with reasonable confidence to be characteristic of the true ${M}_{3}$ emission band. Comparison is made with earlier soft-x-ray results, with band calculations for paramagnetic Ni, and with ion neutralization and photoemission measurements on ferromagnetic Ni. Systematic variations in transition matrix elements and lifetime broadening appear important when relating any experiment with theory, and an aspect of each of these problems has been considered quantitatively. The variation obtained is more severe for the photoemission than for the soft-x-ray analysis. The ion-neutralization and soft-x-ray results appear closer to the single-particle density of states.