Ferromagnetic properties of the degenerate semiconductorPb0.20Sn0.72Mn0.08Te

We analyze the properties of a diluted ferromagnetic semiconductor ${\mathrm{Pb}}_{\mathit{x}}$ ${\mathrm{Sn}}_{1\mathrm{-}\mathit{x}\mathrm{-}\mathit{y}}$ ${\mathrm{Mn}}_{\mathit{y}}$Te for x=0.20 and y=0.08, for the two concentrations of holes p=2.3×${10}^{21}$ ${\mathrm{cm}}^{\mathrm{-}3}$ and p=2.7×${10}^{20}$ ${\mathrm{cm}}^{\mathrm{-}3}$. We determine from the field dependence of the magnetization the magnon contribution to the spontaneous magnetization; this contribution is used to calculate the magnitude of the effective exchange integral ${\mathit{J}}_1$=4.8 K between nearest neighbors for the sample with higher p. The paramagnetic Curie temperature determined theoretically from the magnon contribution to the magnetization agrees within 30% with that obtained from measurements in the paramagnetic regime for the sample with higher p. The magnon contribution to the specific heat is estimated and subtracted from the corresponding data. The large value of the linear specific-heat coefficient γ≊73 mJ/mol ${\mathrm{K}}^2$, as well as the spin reduction ΔS≊0.2±0.05 of the atomic spin S=5/2 of the ${\mathrm{Mn}}^{2+}$ ion indicate an antiferromagnetic coupling of the Kondo type between the valence holes and the magnetic ions.