Spontaneous generation of the electrical voltage in charge-ordered manganite Pr$_{0.6}$Ca$_{0.4}$MnO$_3$

Spontaneous generation of the electrical voltage in a Pr$_{0.6}$Ca$_{0.4}$MnO$_3$ single crystal has been found. The charge and orbital ordering in the crystal takes place at $T_{CO}$ = 240 K, while the antiferromagnetic ordering occurs at $T_N$ = 174 K. As the temperature lowers, spontaneous voltage $U$ increases initially slowly (in the temperature range from 300 K to $T_{CO}$) and then more rapidly (in the range $T_{CO}$–$T_N$). Starting from $T_N$, the voltage $U$ increases exponentially and, at 85 K, reaches 115 mV (in the $ab$ plane) and 6.5 mV (along the $c$ axis). The magnetic field differently affects the voltage $U$ in different temperature ranges: it decreases the value of $U$ in the temperature range of 85–130 K and increases in the range of 130–240 K. It is assumed that the spontaneous voltage is associated with the existence of ferromagnetic and charge orbital ordered clusters of different topologies in the crystal.