Critical properties in single crystals of Pr1-xPbxMnO3

TL;DR

This study analyzes the critical magnetic properties of Pr1-xPbxMnO3 single crystals near the ferromagnetic transition, revealing different behaviors in insulating and metallic phases and indicating magnetic frustration effects.

Contribution

It provides detailed critical exponent analysis for Pr1-xPbxMnO3, highlighting differences between insulating and metallic samples and suggesting magnetic frustration influences.

Findings

Insulating crystal (x=0.23) follows Heisenberg universality class.

Metallic crystal (x=0.30) shows deviations from standard scaling.

Magnetic frustration suppresses magnetic ordering in the metallic phase.

Abstract

The critical properties at the ferromagnetic - paramagnetic transition have been analysed from data of static magnetization measurements on single crystals of Pr1-xPbxMnO3, for x = 0.23 and x = 0.30. In Pr1-xPbxMnO3 the ferromagnetic ordering and the metal-insulator transition do not coincide in parts of the phase diagram. The crystal with x = 0.23 is a ferromagnetic insulator with Curie temperature Tc = 173 K, while the crystal with x =0.30 has Tc = 198 K and remains metallic up to a metal-insulator transition temperature Tmi = 235 K. The dc magnetization measurements were carried out in the field range from 0 to 5 T for an interval in the critical temperature range Tc+_10 K corresponding to a reduced temperature interval 0.003 < epsilon < 0.6. The exponents beta for spontaneous magnetization, gamma for the initial susceptibility above Tc and delta for the critical magnetization isotherm at Tc were obtained by static scaling analysis from modified Arrott plots and by the Kouvel Fisher method for the insulating crystal with composition x = 0.23. The data are well described by critical exponents similar to those expected for the Heisenberg universality class relevant for conventional isotropic magnets Systematic deviations from scaling in the data for the metallic crystal with composition x = 0.30 are demonstrated from effective critical exponents near the assumed ordering transition. The unconventional magnetic ordering in this system indicates the presence of frustrated magnetic couplings that suppresses magnetic ordering and lowers the transition temperature.