Peculiar magnetotransport properties in La0.67Sr0.33MnO3/LaAlO3/SrTiO3

We have investigated the planar Hall effect (PHE) and the anisotropic magnetoresistance (AMR) in La0.67Sr0.33MnO3/LaAlO3/SrTiO3 (LSMO/LAO/STO) and LSMO/STO structures, where the LSMO (LAO) thickness was 13 unit cells (u.c.) and 18 u.c. (8 u.c. and 6 u.c.). The LAO/STO structures under the LSMO layers are conductive, which is consistent with the formation of a two-dimensional electron system (2DES) at the LAO/STO interface. The magnetotransport measurements show that the sign of the PHE coefficient for the LSMO/LAO/STO structures is opposite to that for the LSMO/STO structures, whereas the AMR coefficient, which is generally correlated with the PHE coefficient, is negative for both structures at temperatures below ∼175 K. The LAO/STO structures show no apparent PHE or AMR, and the coefficients obtained thus originate from the LSMO. These results suggest that the 2DES and/or the LSMO/LAO interface affect the PHE in the LSMO layer.