Determination of theGd3+-Gd3+exchange constants from susceptibility measurements onPb1−xGdxTe

Susceptibility measurements have been performed on the semimagnetic semiconductor ${\mathrm{Pb}}_{1\mathrm{-}\mathrm{x}}$ ${\mathrm{Gd}}_{\mathrm{x}}$Te with concentrations 0.01≤x≤0.11 and in the temperature range 1.5 K≤T≤300 K. As a consequence of the rocksalt structure of these compounds, we propose a dominant exchange interaction exerted between next-nearest-neighbor ions. Thus, the susceptibility data are analyzed with good agreement using a two-spin-cluster model for next-nearest-neighbor magnetic ions and a molecular-field model for the other interactions. The results give an exchange constant between next nearest neighbors $J_2$/$k_B$=-1.1±0.1 K, which is in agreement with the previous study by high-field-magnetization measurements.