Unusual features of erbium-based Heusler phases

Heusler alloys ErPd2Sb, ErPd2Bi, ErPdSb and ErPdBi were studied by means of X-ray diffraction, magnetic susceptibility, electrical resistivity, thermoelectric power and Hall effect measurements. All these compounds are paramagnetic down to 1.7K due to localized magnetism of Er3+ ions. Their electrical behavior is governed by the formation of narrow gaps in the electronic band structures near EF. Both electrons and holes contribute to the conductivity, yet the dominant role is played by p-type carriers. The Hall response is strongly dependent on temperature and applied magnetic field, thus reflecting complex character of the underlying electronic structures. The Seebeck coefficient in ErPdSb is of the order of 150μV/K at room temperature making this material promising candidate for thermoelectric applications. Common to all four compounds studied is a rapid drop in the resistivity below 6–8K that seems manifest a phase transition of magnetic or superconducting origin, despite the lack of any corresponding anomalies in the low-temperature magnetic susceptibility and specific heat.