Specific features of temperature dependence of colossal and tunneling magnetoresistance in manganite films

Objectives. This work aims to theoretically and experimentally investigate the specific features of magnetoresistance temperature dependence in nanostructured films of doped manganites. The temperature dependence of electrical resistance for La_0.67Ba_0.33MnO₃ manganite films, grown by laser ablation on various dielectric substrates, is investigated over a wide temperature range.

Methods. Epitaxial La_0.67Ba_0.33MnO₃ films with a thickness of 80 nm were grown by pulsed laser ablation using an АrF excimer laser (a laser wavelength of 247 nm) on single-crystalline SrTiO₃ and ZrO₂(Y₂O₃) substrates. The magnetoresistance properties were measured using a two-probe DC method. The measurements were conducted in magnetic fields up to 8 kOe applied in the film plane, across a temperature range of 80–350 K. To accomplish the research objectives, an empirical magnetoresistance model was applied in two distinct temperature regions: near the magnetic phase transition temperature and in the ground-state region.

Results. Empirical relations for temperature dependence of magnetoresistance for nanostructured La_0.67Ba_0.33MnO₃ films were established, encompassing both the Curie temperature region and the ground-state regime. Our studies revealed that the magnetoresistance of epitaxial single-crystalline La_0.67Ba_0.33MnO₃ films exhibits a sharp peak exclusively near the Curie temperature while remaining negligible in other temperature ranges. Conversely, La_0.67Ba_0.33MnO₃ films with a variant structure demonstrate significant low-temperature magnetoresistance. This effect arises from magnetic-field-induced modifications of the high-frequency conductivity, which results from spin-polarized electron tunneling across structural domain boundaries. A unified empirical model to describe various mechanisms of magnetoresistance in doped manganites is proposed.

Conclusions. For the first time, an empirical model to describe both the colossal and tunneling magnetoresistance in thin films of doped manganites has been developed. This model demonstrates excellent agreement between experimental and calculated data for La_0.67Ba_0.33MnO₃ films with and without a variant structure. The simulation results agree well with experimental data. The findings elucidate the understanding of magnetoresistance mechanisms, contribute to the development of the magnetorefractive effect theory for thin-film manganites, and inform new approaches for controlling charge carrier dynamics in strongly correlated magnetic oxides.

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