Resonant microwave conductivity response to ac current in La0.7Pb0.3MnO3 crystals

An experimental study of the effect of low-frequency transport current on the microwave conductivity of single-crystal La_0.7Pb_0.3MnO₃ is reported. In the absence of an external magnetic field, the microwave conductivity response to a current follows a relaxation behavior. In a nonzero external magnetic field, the response spectrum exhibits a peak of resonant amplitude enhancement. The resonant response has a nonlinear nature. The temperature and field dependences of the main parameters of the microwave response correlate directly with the behavior of the magnetoresistance. The results obtained are analyzed within the oscillator approximation. Electronic phase separation is proposed as a possible mechanism for the current action. Fiz. Tverd. Tela (St. Petersburg) 41, 2187–2192 (December 1999)