Modified Magnetotransport in Digital Manganite Superlattices

We investigate how the series of manganite superlattices, (LaMnO$_{3}$)$_{2n}$(SrMnO$_{3}$)$_{n}$, responds to an out-of-plane magnetic field in order to better understand how the magnetism and magnetotransport are modified in a short period superlattice. The n=1 superlattice shows magnetotransport and magnetic hysteresis similar to the random alloy with positive low field magnetoresistance (MR) due to anisotropic magnetoresistance (AMR) and negative MR at high fields due to colossal magnetoresistance (CMR). However, the n=2 superlattice behaves differently with large negative MR at high fields, and no positive low field MR for T$<$100K. The lack of positive low field MR has also been seen in La$_{2/3}$Sr$_{1/3}$MnO$_{3}$ films with perpendicular magnetic anisotropy, suggesting that the n=2 sample moments contain an out-of-plane, canted or frustrated component at low fields. The reemergence of positive low field MR for the n=2 sample above 100K indicates that the driving force for the different moment orientation is strongly temperature dependent.