Colossal magnetoresistance of La0.35Nd0.35Sr0.3MnO3 epitaxial thin film on (001)ZrO2(Y2O3) substrate over a wide temperature range

Colossal negative magnetoresistance is found over a wide range of temperatures below the Curie point T-C approximate to 240 K in an epitaxial La-0.35 Nd0.35Sr0.3MnO3 film on a single-crystal (001)ZrO2(Y2O3) wafer substrate. Isotherms of the magnetoresistance of this film reveal that its absolute value increases with the field, abruptly in the technical magnetization range and almost linearly in stronger fields. For three epitaxial films of the same composition on (001)LaAlO3, (001)SrTiO3, and (001)MgO substrates, colossal magnetoresistance only occurred near T-C approximate to 240 K and at T < T-C it increased weakly, almost linearly with the field. In the film on ZrO2(Y2O3) substrate the electrical resistivity was almost 1.5 orders of magnitude higher than that in the other three films. It is shown that this increase is attributable to the electrical resistance of the interfaces between microregions having four types of crystallographic orientation, while the magnetoresistance in the region before technical saturation of the magnetization is attributable to tunnelling of polarized carriers across these interfaces which coincide with the domain walls tin the other three films there is one type of crystallographic orientation). The reduced magnetic moment observed for all four samples, which is only 46% of the pure spin value, can be attributed to the existence of magnetically disordered microregions which originate from the large thickness of the domain walls which is greater than the size of the crystallographic microregions and is of the same order as the film thickness. The colossal magnetoresistance near T-C and the low-temperature magnetoresistance in fields exceeding the technical saturation level can be attributed to the existence of strong s-d exchange which is responsible for a steep drop in the mobility of the carriers (holes) and their partial localization at levels near the top of the valence band. Under the action of the magnetic field the carrier mobility increases and they become delocalized from these levels.