Structural, thermal, magnetic, and electronic transport properties of the LaNi2(Ge1−xPx)2system

Abstract

Polycrystalline samples of LaNi2(Ge{1-x}P{x})2 (x = 0, 0.25, 0.50, 0.75, 1) were synthesized and their properties investigated by x-ray diffraction (XRD), heat capacity Cp, magnetic susceptibility chi, and electrical resistivity rho measurements versus temperature T. These compounds all crystallize in the body-centered-tetragonal ThCr2Si2-type structure. The rho(T) measurements indicate that all compositions in this system are metallic. The low-T Cp measurements yield a rather large Sommerfeld coefficient gamma = 12.4(2) mJ/mol K^2 for x = 0 reflecting a large density of states at the Fermi energy that is comparable with the largest values found for the AFe2As2 class of materials with the same crystal structure. The gamma decreases approximately linearly with x to 7.4(1) mJ/mol K^2 for x = 1. The chi measurements show nearly temperature-independent paramagnetic behavior across the entire range of compositions except for LaNi2Ge2, where a broad peak is observed at 300 K from chi(T) measurements up to 1000 K that may arise from short-range antiferromagnetic correlations in a quasi-two-dimensional magnetic system. High-accuracy Pade approximants representing the Debye lattice heat capacity and Bloch-Gruneisen electron-phonon resistivity functions versus T are presented and are used to analyze our experimental Cp(T) and rho(T) data, respectively. The T-dependences of rho for all samples are well-described by the Bloch-Gruneisen model, although the observed rho(300 K) values are larger than calculated from this model. A significant T-dependence of the Debye temperature determined from the Cp(T) data was observed for each composition. No clear evidence for bulk superconductivity or any other long-range phase transition was found for any of the compositions studied.