Exchange interaction in rare-earth-doped IV-VI diluted magnetic semiconductors

The magnetization and magnetic susceptibility of Bridgman-grown ${\mathrm{Sn}}_{1\mathrm{-}\mathit{x}}$ ${\mathrm{Gd}}_{\mathit{x}}$Te samples with values of x up to 0.09 have been measured in fields up to 5.5 T over a temperature range from 2 to 300 K and in fields up to 23 T at 4.2 K. The low-field, high-temperature susceptibility data followed the Curie-Weiss relation with a small Curie temperature. The magnetic-field dependence of the magnetization was fitted to an expression containing a Brillouin function, representing isolated magnetic ions, plus a term representing pair interactions. Both the susceptibility and the high-field magnetization data indicated a weak antiferromagnetic coupling among Gd ions. These results are compared with our previously obtained exchange parameters for ${\mathrm{Pb}}_{1\mathrm{-}\mathit{x}}$ ${\mathrm{Gd}}_{\mathit{x}}$Te and ${\mathrm{Pb}}_{1\mathrm{-}\mathit{x}}$ ${\mathrm{Eu}}_{\mathit{x}}$Te. The exchange interaction in ${\mathrm{Sn}}_{1\mathrm{-}\mathit{x}}$ ${\mathrm{Gd}}_{\mathit{x}}$Te is larger than in PbTe-based, rare-earth-doped chalcogenides, in agreement with the smaller cation-anion spacing in SnTe-based compounds. A ferromagnetic or spin-glass ordering due to the possible Ruderman-Kittel-Kasuya-Yosida interaction in ${\mathrm{Sn}}_{1\mathrm{-}\mathit{x}}$ ${\mathrm{Gd}}_{\mathit{x}}$Te with high hole concentration was not observed.