Relaxation of magnetoresistance of single-crystalline (La$_{0.5}$Eu$_{0.5}$)$_{0.7}$Pb$_{0.3}$MnO$_3$ in a pulsed magnetic field

The magnetoresistance (MR) of substituted lanthanum manganite (La$_{0.5}$Eu$_{0.5}$)$_{0.7}$Pb$_{0.3}$MnO$_3$ has been measured in a pulsed magnetic field with amplitude $H$ = 250 kOe at various temperatures. It is established that temperature dependence of the MR relaxation parameter $\tau(T)$ is correlated with temperature dependence of the electric resistance $R(T)$. A mechanism of relaxation is proposed that is related to the relaxation of conducting and dielectric phases in the volume of a sample under the conditions of phase separation. It is shown that the behavior of $\tau$ is related to the number of phase boundaries in the volume.