Electrical transport properties of semimetallic GdX single crystals (X=P, As, Sb, and Bi)

The large single crystals of stoichiometric and nonstoichiometric Gd monopnictides GdX (X=P, As, Sb, and Bi) are grown by the mineralization method (for X=P and As) and Bridgman method (for X=Sb and Bi). A systematic investigation of the transport properties of GdX single crystals is presented. We report on measurements of the electric resistivity ρ(T), magnetoresistance ρ(H), and Hall effect performed on the stoichiometric and nonstoichiometric samples at temperatures between 1.6 and 300 K in magnetic fields up to 10 T. The stoichiometric samples behaved as the well-compensated semimetals that order antiferromagnetically at Néel temperatures T_N=15.9 K for GdP, 18.7 K for GdAs, 23.4 K for GdSb, and 25.8 K for GdBi. The transverse magnetoresistance measured at low temperature follows a ρ(H)~H² law, and a larger positive ratio MRR=[ρ(H)-ρ(0)]/ρ(0) is observed at 10 T for the four stoichiometric samples. The temperature dependence of the resistivity can be explained by the d-f Coulomb exchange interaction at lower temperatures. The Hall-effect measurements yield a carrier concentration n=2.1×10²⁰ cm^-3 for GdAs and n=4.2×10²⁰ cm^-3 for GdSb, which are in a good agreement with the de Haas-van Alphen effect measurements. The nonstoichiometric samples showed some anomalies that could be explained qualitatively by the model of trapped magnetic polaron.