A model for spin-polarized transport in perovskite manganite bi-crystal grain boundaries

We have studied the temperature dependence of low-field magnetoresistance and current-voltage characteristics of a low-angle bi-crystal grain boundary junction in perovskite manganite La2/3Sr1/3MnO3 thin film. By gradually trimming the junction we have been able to reveal the non-linear behavior of the latter. With the use of the relation MGB ∝ Mbulk √ MR we have extracted the grain boundary magnetization. Further, we demonstrate that the built-in potential barrier of the grain boundary can be modelled by Vbi ∝ M 2 bulk − M 2 GB . Thus our model connects the magnetoresistance with the potential barrier at the grain boundary region. The results indicate that the band-bending at the grain boundary interface has a magnetic origin. Recent studies have shown that grain boundaries (GBs) in polycrystalline perovskite manganites, so called colossal-magnetoresistance (CMR) materials, give raise to a low-field magnetoresistance.[1, 2] To analyze the contribution from a single grain boundary on magnetoresistance, thin film bi-crystal structures have previously been applied by several research groups.[3, 4, 5, 6, 7, 8, 9, 10, 11] Supported by such studies Evetts et al [12] have suggested that the lowfield magnetoresistance MR associated with GBs relates to the magnetization MGB of the interface region. In their model they assume that the resistivity ρ depends on the magnetization M as ρ ∝ ρ0 exp[−M/M B] (MB represents the bulk magnetization) and hence the magnetoresistance MR ≡ (ρ0 − ρ)/ρ0 can for the GB be determined as