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

Electron paramagnetic resonance (EPR) measurements were carried out to study the appearance of magnetic order in the ground states of both La0.67Ca0.33MnO3 (PCMO) and Pr0.65Ca0.35MnO3 (PCMO) thin films. LCMO undergoes the transition of the paramagnetic insulating phase into the metallic ferromagnetic phase below the Curie temperature (T-c = 260 K). The PCMO films also undergo the transition into the ferromagnetic phase when the temperature is lowered through the critical value (T-c = 120 K). Below T-c the EPR spectrum of both films splits into lines that shift to the low magnetic resonance field with decrease in temperature. The temperature dependence of the resonance magnetic field in both EPR spectra obeys the critical behavior of a second-order phase transition, corresponding to the appearance of the spontaneous magnetic moment. In contrast to the bulk PCMO sample, PCMO thin films prepared by the sol-gel method shows only one magnetic transition. (C) 2000 Elsevier Science B.V. All rights reserved.