Electron momentum distribution and spin density of ferromagnetic iron studied by spin-polarised positron annihilation

The authors report the first study of the Fermi surface topology, electron momentum density and spin momentum density in ferromagnetic iron using two-dimensional angular correlation of polarised positron annihilation radiation. A calculation made in the independent-particle model was obtained from the self-consistent linear muffin-tin orbital method. Comparison between experiment and calculation reveals marked discrepancies which are due to both electron-electron and electron-positron correlation effects. Analysis of experimental distributions shows that the large N-centred hole pocket of minority third band does not exist in contrast with the self-consistent calculation results. A parametrised band-structure calculation has been performed to account for the electron-electron correlation effects. Distributions resulting from this procedure were in better agreement with experiment than the self-consistent ones. Once again the nature of electron-positron correlation effects is found to resemble those observed by Sing et al. for nickel. This confirms the systematic trends of electron-positron correlation effects for localised d electrons. The correct description of the relative spin momentum density distribution requires different enhancement factors for majority and minority electron bands.