Magnetic Field Dependence of the Specific Heat of Pb$_{1-x}$Gd$_{x}$Te

We have measured the magnetic specific heat, C$_{m}$, of Pb$_{1-x}$Gd$_{x}$Te (x = 0.033 and 0.054) at magnetic fields up to 2 T at temperatures from 0.4 to 9 K. This study is complementary to our magnetization measurements on the same system. The samples were prepared as bulk single crystals by the Bridgman method and were n-type with carrier concentrations of about 1 x 10$^{19}$ cm$^{-3}$. The specific heat measurements were made using a Quantum Design PPMS system. We saw evidence for a maximum in C$_{m}$, which shifted to higher temperatures and became broader with increasing magnetic field. At zero magnetic field this maximum is expected to occur below 0.4 K for both samples and will be several times higher than that predicted by a model of superexchange interactions between nearest neighbors, which was based on previous experiments on Pb$_{1-x}$Eu$_{x}$Te.$^{1}$ The present data will be compared with a model that takes into account the spin splitting of the ground state of the individual Gd ions, possibly due to local lattice distortions. $^{1}$ M. G\'{o}rska, A. Lusakowski, A. Jedrzejczak, Z. Golacki, J. R. Anderson, H. Balci, Acta Phys. Pol. A \textbf{105}, 631 (2004).