Single particle excitations and electronic structure of ferromagnets in the near-surface region

Abstract

The electronic structure underlying the magnetic properties of itinerant ferromagnets currently receives much interest. Major experimental issues are the determination of the spin-split band-structure and its temperature behaviour, and the measurement of elementary excitations specific to itinerant ferromagnets (Stoner excitations). Here we report on measurements of the dispersion of spin-split empty bands in iron, obtained by spin-polarized inverse photoemission. The behaviour of particular band states on approaching the Curie temperature was investigated, and a “collapsing band behaviour” (decreasing energy splitting with increasing temperature) was found, as well as “non-collapsing” behaviour (constant splitting) at particular points in the Brillouin zone. Specific surface features are observed in the inverse photoemission spectra and their temperature induced changes. Stoner excitations (i.e. electron-hole pair excitations with spin-flip) are or great importance for the theory of ferromagnets, but have in general not been accessible to experimental investigations. It is demonstrated that by means of exchange processes in high-resolution spin-polarized electron energy loss spectroscopy the Stoner excitations in Ni and Fe may be investigated in detail. Examples include the Stoner spectrum in Ni at near zero momentum transfer and in iron at finite momentum.