The spin-polarized electron momentum distributions in the Cr-based chalcogenide spinels ${\mathrm{Fe}}_{1-x}{\mathrm{Cu}}_x{\mathrm{Cr}}_2{\mathrm{S}}_4$ $\mathrm{}(x=0.0,0.5,1.0\mathrm{})\mathrm{}$ have been measured using a magnetic Compton scattering technique at $T=10\mathrm{}\mathrm{K}.$ The experimental magnetic Compton profiles have been compared with the results from electronic structure calculations performed using the full potential linearized augmented plane-wave method. The theoretical analysis includes a decomposition of the various orbital and atomic contributions. For $x=0.0\mathrm{}$ and 0.5 sample compositions, the results show that the magnetic moments of the tetrahedrally coordinated ${\mathrm{Fe}}^{2+}$ (for $x=0.0)$ and ${\mathrm{Fe}}^{3+}$ (for $x=0.5)$ with spin moments of $3.66{\mu }_B$ (for $x=0.0)$ per formula unit $\left({\mathrm{FU}}^{-1}\right)$ and $1.6{\mu }_B$ ${\mathrm{FU}}^{-1}$ (for $x=0.5),$ are aligned antiparallel to those of the octahedrally coordinated ${\mathrm{Cr}}^{3+}$ with spin moments of $5.0{\mu }_B$ ${\mathrm{FU}}^{-1}$ (for $x=0.0)$ and $4.82{\mu }_B$ ${\mathrm{FU}}^{-1}$ (for $x=0.5).\mathrm{}$ In the ferromagnetic system for $x=1.0,$ the Cr moment is found to be $5.28{\mu }_B$ ${\mathrm{FU}}^{-1}.$

• Received 6 April 2002

DOI:https://doi.org/10.1103/PhysRevB.66.100407