Magnetic, transport, and thermal properties of the half-Heusler compounds ErPdSb and YPdSb

The half-Heusler compounds ErPdSb and YPdSb were studied by means of x-ray diffraction, magnetic susceptibility, electrical resistivity, magnetoresistivity, thermoelectric power, Hall effect, thermal conductivity, and specific heat measurements, performed in the temperature range $1.5--300\phantom{\rule{0.3em}{0ex}}\mathrm{K}$ and in magnetic fields up to $12\phantom{\rule{0.3em}{0ex}}\mathrm{T}$. The Er-based compound is a paramagnet down to $1.7\phantom{\rule{0.3em}{0ex}}\mathrm{K}$ and shows localized magnetism of ${\mathrm{Er}}^{3+}$ ions, while YPdSb exhibits a weak diamagnetic behavior. The crystal field effect in ErPdSb brings about a distinct Schottky anomaly in the specific heat. The total splitting of the erbium $^{4}I_{15∕2}$ multiplet in a cubic crystal field potential is of the order of $200\phantom{\rule{0.3em}{0ex}}\mathrm{K}$, with a doublet being the ground state. Electrical properties of ErPdSb and YPdSb are governed by the formation of narrow gaps in the electronic band structures very close to the Fermi level. The Hall effect measured for ErPdSb indicates a complex electronic structure with multiple electron and hole bands with different temperature and magnetic field variations of carrier concentrations and mobilities. The thermal conductivity of ErPdSb is relatively low and dominated by the phonon contribution. At room temperature the Seebeck coefficient is of order $150\phantom{\rule{0.3em}{0ex}}\ensuremath{\mu}\mathrm{V}∕\mathrm{K}$ for Er- and $200\phantom{\rule{0.3em}{0ex}}\ensuremath{\mu}\mathrm{V}∕\mathrm{K}$ for Y-based compound, respectively, making these materials promising candidates for thermoelectric applications. This conjecture is supported by the value of the figure of merit of ErPdSb, which is about 0.15 at room temperature.