ИСТИНА

It is known that in Pr1-xCaxMnO3 manganites the ferromagnetic metallic phase is absent. In the concentration area of 0.3 < x < 0.5 an inhomogeneous magnetic insulating ground state takes place, where charge and orbital ordered antiferromagnetic phase of CE-type coexists with the ferromagnetic phase. In our work we have studied Pr0.6Ca0.4MnO3 single crystal grown by the floating zone method. In this compound charge and orbital ordering occurs at TCO = 220 K, and an antiferromagnetic ordering occurs at TN = 150 K. In this sample we have found the spontaneous generation of voltage (SGV). The voltage observed between the ends of the sample are considered as spontaneous since the current sources in a closed circuit are absent. The voltage value depends on the cooling rate of the sample. SGV increases with decreasing temperature, at first slowly (in the temperature interval 300 K  TCO), then more rapidly (TCO  TN). Starting from TN SGV is increasing exponentially and reaches a giant value of 5.2 mV at 85 K (the lowest temperature at which the measurements were performed) at cooling rate 5.6 K/min. The magnetic field influences on SGV value within the temperature range 80<T<150 K only. SGV value is reduced by 2.5% at a magnetic field of 10 kOe at 80 K. We are supposed that SGV is connected with the existence in the sample of areas having different concentration of charge carriers.