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 temperatu res 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. I sotherms of the magnetoresistance of this film reveal that its absolute val ue increases with the field, abruptly in the technical magnetization range and almost linearly in stronger fields. For three epitaxial films of the sa me composition on (001)LaAlO3, (001)SrTiO3, and (001)MgO substrates, coloss al 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 Zr O2(Y2O3) substrate the electrical resistivity was almost 1.5 orders of magn itude higher than that in the other three films. It is shown that this incr ease 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 magnetiz ation is attributable to tunnelling of polarized carriers across these inte rfaces 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, ca n be attributed to the existence of magnetically disordered microregions wh ich originate from the large thickness of the domain walls which is greater than the size of the crystallographic microregions and is of the same orde r as the film thickness. The colossal magnetoresistance near T-C and the lo w-temperature magnetoresistance in fields exceeding the technical saturatio n 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 th eir partial localization at levels near the top of the valence band. Under the action of the magnetic field the carrier mobility increases and they be come delocalized from these levels.