  Magnetoresistance of substituted lanthanum manganite (La0.5Eu0.5)0.7Pb0.3MnO3
in the pulse magnetic field H = 25 T was measured at different temperatures.
Magnetoresistance relaxation with a characteristic time of 10 -3 s was found.
It has been established that the temperature dependence of the relaxation
parameter {\tau}(t) at different temperatures correlates with the temperature
dependence of electrical resistance R(T). The proposed relaxation mechanism is
related to relaxation of conducting and dielectric phases in the sample volume
under phase stratification conditions. It is shown that relaxation parameter
{\tau} reflects the number of boundaries in the volume and not the ratio
between phase fractions.
