Ferromagnetism, superconductivity and secondary phases in the dilute magnetic semiconductor Pt1−xRExSb2 (RE = La, Ce, Gd, Yb)

We have measured the electrical transport, heat capacity, and magnetic properties of single crystals of semiconducting PtSb2, doped with rare earth ions. Carrier concentrations in the doped crystals range from 1017 to 1020 cm−3, and in most cases, metallic resistivity was observed. Moment densities of 1020-1023μB/cm3 were found for crystals doped with magnetic rare earths, and diamagnetic behavior for those doped with non-magnetic rare earths. Weak superconductivity and ferromagnetic order were observed separately in many of the doped crystals, and electron microscopy studies reveal that they likely originate with secondary surface phases. Accordingly, surface etching suppressed both the ferromagnetic and superconducting behaviors. Nonetheless, electrical transport and heat capacity measurements of the doped crystals suggest that the bulk electronic properties are modified relative to stoichiometric PtSb2, making this a potentially interesting system for studying magnetism in a low carrier density environment.