range of temperatures below the Curie point TC
240 K in a single-crystal La0.35Nd0.35Sr0.3MnO3 film on a single-crystal (001)ZrO2(Y2O3) wafer substrate is discussed. 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 single-crystal films of the same composition on (001)LaAlO3, (001)SrTiO3,
and (001)MgO substrates, colossal magnetoresistance only occurred near TC
240 K and at T < TC it increased weakly, almost linearly, with the field. In the film on a 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 orienta-
tions, while the magnetoresistance in the region before technical saturation of the magnetization is attributable
to tunneling of polarized carriers across these interfaces which coincide with the domain walls (in the other
three films there is one type of crystallographic orientation). The reduced magnetic moment observed for all
four samples, being only 46% of the pure spin value, can be attributed to the existence of magnetically disor-
dered 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 magnetoresis-
tance near TC 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 carrier mobility
(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. © 2000 MAIK “Nauka/Inter-
periodica”.