Photoemission Studies of the Electronic Structure of Cobalt

Abstract

Photoemission measurements have been made on cobalt to study major features of its electronic structure over a large energy range. In the spectral range studied ($7.4 \mathrm{eV}\ensuremath{\le}h\ensuremath{\nu}\ensuremath{\le}11.6 \mathrm{eV}$), nondirect transitions dominate. The optical density of states is determined from the photoemission and optical data. Peaks are found in the valence-band structure at about 0.3, 2.4, and 5.2 eV below the Fermi level, and no structure is found in the conduction band for $4.5 \mathrm{eV}\ensuremath{\le}E\ensuremath{-}{E}_{f}\ensuremath{\le}115 \mathrm{eV}$. The $\ensuremath{\omega}\ensuremath{\sigma}$ curve is fitted reasonably well using the optical density of states and assuming nondirect transitions. A strong similarity is found between the optical density of filled states for Co and that of Ni and Fe. Thus the optical density of states for Fe, Co, and Ni do not seem to be related via the rigid-band model. A discussion is given on these data and their relevance to other related results.