Heisenberg-like critical properties in ferromagneticNd1−xPbxMnO3 single crystals

Abstract

Static magnetization for single crystals of insulatingNd0.85Pb0.15MnO3 and marginallyconducting Nd0.70Pb0.30MnO3 has been studied around the ferromagnetic to paramagnetic transition temperatureTC. Results of measurements carried out in the critical range|(T−TC)/TC|≤0.1 are reported.Critical exponents β and γ for the thermal behaviour of magnetization and susceptibility have been obtainedboth by modified Arrott plots and the Kouvel–Fisher method. The exponentδ independently obtained from the critical isotherm was found to satisfy the Widom scaling relationδ = γ/β+1. For both compositions the values of exponents are consistent with those expected forisotropic magnets belonging to the Heisenberg universality class with short-range exchangein three dimensions. Correspondingly, the specific heat displays only a cusp-like anomaly atthe critical temperature of these crystals which is consistent with an exponentα<0. The results show that the ferromagnetic ordering transition inNd1−xPbxMnO3 in thecomposition range 0.15≤x≤0.40 is continuous. This mixed-valent manganite displays the conventional properties of a Heisenberg-likeferromagnet, irrespective of the differing transport properties and in spite of low ordering temperaturesTC = 109 and147.2 K for x = 0.15 and 0.30, respectively.