Magnetic tetrahedral intrasublattice interactions in the spinel family ${\mathrm{Fe}}_x{\mathrm{Cu}}_{1-x}{\mathrm{Rh}}_2{\mathrm{S}}_4$

Several compounds of the spinel ${\mathrm{Fe}}_x{\mathrm{Cu}}_{1-x}{\mathrm{Rh}}_2{\mathrm{S}}_4$ with $x<~0.94$ have been prepared in order to study the magnetic interactions within the tetrahedral sites. The samples were investigated by x-ray, magnetization, and Mössbauer measurements at temperatures between 4.2 and 300 K. All the samples become antiferromagnets. No distortion of the spinel lattice was observed at any temperature. Ordering of the copper and iron ions for $0.46<~x<~0.7$ has been detected by an x-ray technique. Iron-rich compounds ($0.5<x<~0.94$), cooled to 4.2 K in an external magnetic field of 18 kOe, exhibit remanences and displaced hysteresis loops reminiscent of spin glasses. Both susceptibility and isomer-shift measurements indicate a gradual change in valence state from ferric to ferrous iron as $x$ is increased from 0.6 towards 1.0. Energy-band diagrams, consistent with the data, are proposed for the series.