Magnetic transitions in thin films of La0.67Ca0.33MnO3 and Pr0.65Ca0.35MnO3

Electron paramagnetic resonance (EPR) measurements were carried out to stud y the appearance of magnetic order in the ground states of both La0.67Ca0.3 3MnO3 (PCMO) and Pr0.65Ca0.35MnO3 (PCMO) thin films. LCMO undergoes the tra nsition of the paramagnetic insulating phase into the metallic ferromagneti c phase below the Curie temperature (T-c = 260 K). The PCMO films also unde rgo the transition into the ferromagnetic phase when the temperature is low ered through the critical value (T-c = 120 K). Below T-c the EPR spectrum o f both films splits into lines that shift to the low magnetic resonance fie ld with decrease in temperature. The temperature dependence of the resonanc e magnetic field in both EPR spectra obeys the critical behavior of a secon d-order phase transition, corresponding to the appearance of the spontaneou s magnetic moment. In contrast to the bulk PCMO sample, PCMO thin films pre pared by the sol-gel method shows only one magnetic transition. (C) 2000 El sevier Science B.V. All rights reserved.