Low Temperature Transport and Specific Heat Studies of Nd_{1-x}Pb_{x}MnO_{3} Single Crystals

TL;DR

This study investigates the low-temperature electrical transport and specific heat of Nd_{1-x}Pb_{x}MnO_{3} single crystals, revealing metal-insulator transition points, electron scattering mechanisms, and magnetic effects influencing thermodynamic properties.

Contribution

It provides detailed analysis of transport and heat capacity across doping levels, identifying the critical concentration for metal-insulator transition and the influence of magnetic ordering on electronic properties.

Findings

Critical doping for metal-insulator transition at x ~ 0.33.

Electron-electron scattering dominates resistivity in metallic samples.

Enhanced gamma value linked to Nd magnetic ordering.

Abstract

Electrical transport and specific heat properties of Nd_{1-x}Pb_{x}MnO_{3} single crystals for 0.15 < x 0.5 have been studied in low temperature regime. The resistivity in the ferromagnetic insulating (FMI) phase for x < 0.3 has an activated character. The dependence of the activation gap Delta on doping x has been determined and the critical concentration for the zero-temperature metal-insulator transition was determined as x_{c} ~ 0.33. For a metallic sample with x=0.42, a conventional electron-electron (e-e) scattering term proportional T^{2} is found in the low-temperature electrical resistivity, although the Kadowaki-Woods ratio is found to be much larger for this manganite than for a normal metal. For a metallic sample with x=0.5, a resistivity minimum is observed for x= 0.5. The effect is attributed to weak localization and can be described by a negative T^{1/2} weak-localization contribution to resistivity for a disordered three-dimensional electron system. The specific heat data have been fitted to contributions from free electrons (gamma), spin excitations (beta_{3/2}), lattice and a Schottky-like anomaly related to the rare-earth magnetism of the Nd ions. The value of gamma is larger than for normal metals, which is ascribed to magnetic ordering effects involving Nd. Also, the Schottky-like anomaly appears broadened and weakened suggesting inhomogeneous molecular fields at the Nd-sites.