Overdamped interlayer exchange coupling and disorder-dominated magnetoresistance in La0.7Ca0.3MnO3/LaNiO3 superlattices

Magnetization and magnetoresistance (MR) measurements are reported on superlattices consisting of alternate layers of 20 unit cell (u. c.) thick La0.7Ca0.3MnO3 (LCMO) and n u. c. LaNiO3 (LNO), where n varies from 1 to 10. The saturation field (H-s) and remnant magnetization (M-r) show antiferromagnetic (AF) interlayer coupling for n less than or equal to 2 followed by an overdamped oscillatory behavior with a period of approximate to 4 u.c. with the increasing n. The low-temperature MR of the AF-coupled superlattices is characterized by a steep increase up to a critical field H-s(*) (approximate to H-s) followed by a similar to H-alpha (alpha < 1.0) dependence, whereas in the ferromagnetically coupled samples the MR rises monotonically as similar to H-alpha with no H-s*. We attribute the overdamped oscillations in M-r and H-s, and the dual nature of MR to disorder modified quantum interference in the spacer layers.