Single crystal growth and some properties of HgCr2−xInxSe4 solid solutions

Indium was found to substitute for Cr ions to a limited extent in the ferromagnetic spinel HgCr₂Se₄. For the solid solution HgCr_2−xIn_xSe₄, the maximum value of x was determined to be 0·45. The lattice parameter increases with increasing x from a₀=10·743 Å for x=0, to a₀=10·836 Å for x=0·45. The u-parameter is 0·390 for all compositions. The single crystals of HgCr_2−xIn_xSe₄ studied were all grown by chemical transport either from an HgCr_2−xIn_xSe₄−CrCl₃ system or from an HgCr₂ Se₄−CrCl₃−InCl₃ system. In the former system, the fractionation of In during crystal growth was quite marked in that the In content in the large single crystals was always significantly lower than in the polycrystalline powder. Attempts to grow single crystals with an In concentration near the solubility limit were not successful. The maximum lattice parameter obtained for single crystals grown by chemical transport was 10·777 Å, which corresponds to x=0·17. The Curie temperature of the HgCr_2−xIn_xSe₄ single crystals grown was found to be a monotonically decreasing function of the In content. The electrical resistivity of the single crystals grown had a maximum near the Curie temperature just as did the ‘In-doped’ HgCr₂Se₄ which had been previously grown by chemical transport from Hg_1−nIn_nCr₃Se₄ powders (y≤0·02) using CrCl₃ as a transport agent. The magnetoresistance of the single crystals was negative and had a maximum near T_c, as was also the case for the ‘In-doped’ HgCr₂Se₄. However, the increase in resistivity from room temperature to T_c for the present crystals was found to be markedly lower than for the ‘In-doped’ HgCr₂Se₄. indicating that for the system HgCr_2−xIn_xSe₄ the conduction is nearly metallic in the temperature range studied.