Critical properties in single crystals of Pr1-xPbxMnO3

The critical properties at the ferromagnetic-paramagnetic transition have been analyzed from data of static magnetization measurements on single crystals of $Pr_{1-x}Pb_xMnO_3$ for x=0.23 and x=0.30. In $Pr_{1-x}Pb_xMnO_3$, 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 $T_C$=167 K, while the crystal with x =0.30 has $T_C$=198 K and remains metallic up to a metal-insulator transition temperature $T_{MI}$=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\pm 10 K corresponding to a reduced temperature interval 0.0030 < |\varepsilon|< 0.06. The exponents $_\beta$ for spontaneous magnetization, \gamma for the initial susceptibility above $T_C$, and \delta for the critical magnetization isotherm at $T_C$ 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 suggests the presence of frustrated magnetic couplings that suppress magnetic ordering and lower the transition temperature.