Calculation of the momentum density in ferromagnetic nickel

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Abstract
A band-structure calculation on the basis of Hubbard's approximation scheme has been made of the momentum-density distribution for positron annihilation and Compton scattering in ferromagnetic nickel. Graphs are shown of the contributions of the various bands for both spin directions, of the total momentum density, and of the spin density observable with polarized positrons. Owing to the symmetry of the wave functions the only pieces of Fermi surface observable with these techniques are the large sheets in the sixth majority- and minority-spin bands, and the minority-spin hole pocket in the third band. A comparison of the predicted angular correlation with experiment shows that the calculation somewhat overestimates the high-momentum region.