Magnetic and thermodynamic properties of selected SmT2X2 ternaries

Four ternary SmT2X2 (T = Fe, Co; X = Si, Ge) compounds have been synthesized in polycrystalline form, characterized by X-ray powder diffraction and studied in detail by means of magnetization and specific heat measurements in the temperature range 200–300 K and in magnetic fields up to 9 T. All the four compounds have been found to crystallize in the tetragonal ThCr2Si2-type structure with the space group I4/mmm. Both germanides, SmCo2Ge2 and SmFe2Ge2, exhibit a susceptibility maximum at ∼14 and ∼6 K, respectively, and a corresponding specific heat anomaly, which can be attributed to the transition from paramagnetic to antiferromagnetic state. Whereas the magnetization of SmCo2Ge2 is nearly linear with magnetic field increasing up to 9 T, the other germanide at 2 K undergoes a clear metamagnetic transition in magnetic fields above 2 T. Also in case of SmCo2Si2 magnetization and specific heat data can be conceived with antiferromagnetism at temperatures below TN ∼ 17 K. The SmFe2Si2, however, is apparently ferromagnetic below ∼3.5 K as evidenced by anomalies in the temperature dependence of the specific heat and ac-susceptibility and their evolution in magnetic fields, as well as by the evolution of magnetization curves with temperature.