Field dependence of colossal magnetoresistance in magnetic fields up to 50 T

The magnetoresistance (MR) of La0.7Sr0.3MnO3 and La0.7Ca0.3MnO3 epitaxial films and of a La0.75Sr0.25MnO3 single crystal were measured in pulsed magnetic fields up to 50 T over a wide temperature range. MR data have been analysed utilizing the recently suggested Brillouin scaling model. The model applies well in the paramagnetic state, where results prove the presence of superparamagnetic clusters. Near the ferromagnetic ordering temperature, systematic deviations in particular in larger fields indicate that the simple model fails there. The temperature-dependent cluster size parameter is similar for our samples, but differs essentially from that obtained earlier for half-doped manganites