Colossalmagnetoresistance of La0.35Nd0.35Sr0.3MnO3epitaxial thin film on (001)ZrO2(Y2O3) substrate over awide temperature range

Abstract

Colossal negative magnetoresistance is found over a wide range oftemperatures below the Curie point TC≈240 K in an epitaxialLa0.35Nd0.35Sr0.3MnO3 film on a single-crystal(001)ZrO2(Y2O3) wafer substrate. Isotherms of themagnetoresistance of this film reveal that its absolute valueincreases with the field, abruptly in the technical magnetizationrange and almost linearly in stronger fields. For three epitaxialfilms of the same composition on (001)LaAlO3, (001)SrTiO3, and(001)MgO substrates, colossal magnetoresistance only occurred nearTC≈240 K and at T<TC it increased weakly, almostlinearly with the field. In the film on ZrO2(Y2O3)substrate the electrical resistivity was almost 1.5 orders ofmagnitude higher than that in the other three films. It is shown thatthis increase is attributable to the electrical resistance of theinterfaces between microregions having four types ofcrystallographic orientation, while the magnetoresistance in theregion before technical saturation of the magnetization isattributable to tunnelling of polarized carriers across theseinterfaces which coincide with the domain walls (in the other threefilms there is one type of crystallographic orientation). Thereduced magnetic moment observed for all four samples, which is only46% of the pure spin value, can be attributed to the existence ofmagnetically disordered microregions which originate from the largethickness of the domain walls which is greater than the size of thecrystallographic microregions and is of the same order as the filmthickness. The colossal magnetoresistance near TC and thelow-temperature magnetoresistance in fields exceeding the technicalsaturation level can be attributed to the existence of strong s-dexchange which is responsible for a steep drop in the mobility ofthe carriers (holes) and their partial localization at levels nearthe top of the valence band. Under the action of the magnetic fieldthe carrier mobility increases and they become delocalized fromthese levels.