Abnormal Spin Hall magnetoresistance in ultra-thin Pt/LSMO

Thin film bilayer systems comprised of a normal metal (NM) and a ferromagnetic insulator (FI) revealed a new type of magnetoresistance called spin Hall magnetoresistance (SMR) [1]. Very recently, a negative SMR was reported in antiferromagnetic (AFM) insulator [2]. Competing effects may mix in the system and might complicate the data analysis and interpretation. Here we present a case of ultra-thin Pt/LSMO, in which the magnetic state of the LSMO layers depends sensitively on the thickness. Specifically, 6 unit cell (UC) LSMO is a magnetic insulator with Curie temperature (Tc) of 120 K and 3 UC LSMO is an antiferromagnetic insulating. In the Pt/6UC LSMO system, the magnetoresistance (MR) includes contributions from both the anisotropic magnetoresistance (AMR) and SMR effects below curie temperature. Strikingly, the MR increases with temperature even up to temperatures above Tc, which is distinctly different from the case of Pt/YIG [3]. Anomalous Hall effect was also performed showing consistentency with SMR measurement. In the Pt/3UC LSMO system, the SMR signal also shows similar abnormal temperature dependence. We attribute the underlying mechansim to the competing effects from the coexisting electronic phases in the LSMO system.