Rare earth manganites demonstrate unusual electrical properties due to a strong interplay between spin, charge and orbital degrees of freedom. During the last years, major attention was paid to resistance change of both manganite films demonstrating various crystalline quality and related heterostructures by applying a permanent magnetic field (colossal magnetoresistance, tunneling magnetoresistance, grain boundary magnetoresistance etc). Recent investigation of polycrystalline manganite films in a microwave electrical field gave insightful information about their grain boundaries. However, up to now, microwave radiation-induced resistance change of the manganite films was studied taking into account a key role of high frequency electrical field on electrical properties of the manganites. Here we present new experimental evidence indicating importance of magnetic field component of microwave field (f = 9.4 GHz) on magnetoresistive properties of polycrystalline manganite films. Polycrystalline La_0.7Ca_0.3MnO₃ films were grown on lucalox substrates by on-axis pulsed laser deposition. Microwave measurements revealed different character of the temperature-dependent electrical resistance of polycrystalline LCMO films placed in various positions of a waveguide. In the center of the waveguide, microwave electric field should determine resistance change under the influence of H₁₀ wave. Near the narrow wall of the waveguide, where the electric component of the H₁₀ wave decreases notably, the longitudinal microwave magnetic component should take part in the magnetoresistance of the polycrystalline LCMO film that was proved experimentally. Additional experiments with applied external permanent magnetic field confirmed the influence of microwave magnetic field on magnetoresistance of polycrystalline LCMO films.

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