Compton study of ${\mathrm{Ni}}_{75}{\mathrm{Cu}}_{25}$ and ${\mathrm{Ni}}_{75}{\mathrm{Co}}_{25}$ disordered alloys: Theory and experiment

We present first-principles computations of ferromagnetic electronic structures and spin-resolved Compton profiles along the three high-symmetry directions in ${\mathrm{Ni}}_{75}{\mathrm{Cu}}_{25}$ and ${\mathrm{Ni}}_{75}{\mathrm{Co}}_{25}$ disordered alloys, together with the corresponding Compton measurements from single-crystal specimens with a ${}^{137}\mathrm{Cs}$ source. The theoretical results are based on the use of the charge- and spin-self-consistent Korringa-Kohn-Rostoker coherent-potential-approximation framework to treat disorder, and the local spin-density scheme for incorporating exchange-correlation effects; the lattice constants in all cases are obtained by minimizing the total energy. The majority-spin spectrum of Ni undergoes relatively small changes upon alloying with Cu or Co, and the associated majority-spin contribution to the Compton profiles of Ni, ${\mathrm{Ni}}_{75}{\mathrm{Cu}}_{25}$ and ${\mathrm{Ni}}_{75}{\mathrm{Co}}_{25}$ is nearly the same. In comparing theory and experiment, we focus on anisotropies in Compton profiles, and find the overall agreement with respect to the $J_{111}-J_{100},$ $J_{111}-J_{110},$ and $J_{110}-J_{100}$ anisotropies in ${\mathrm{Ni}}_{75}{\mathrm{Cu}}_{25}$ as well as ${\mathrm{Ni}}_{75}{\mathrm{Co}}_{25}$ to be reasonable, although some significant discrepancies around $p_z=0\mathrm{}$ are notable. We show clearly that the momentum resolution of 0.4 a.u. (full width at half maximum) of the present experiment washes out some of the fine structure in the Compton spectra, and that these spectral features should be accessible via higher resolution measurements with a synchrotron light source.