Extraordinary Hall resistance and unconventional magnetoresistance in Pt/LaCoO3 hybrids

We report an investigation of transverse Hall resistance and longitudinal resistance on Pt thin films sputtered on epitaxial LaCoO${}_3$ (LCO) ferromagnetic insulator films. The LaCoO${}_3$ films were deposited on several single crystalline substrates [LaAlO${}_3$ (LAO), (La,Sr)(Al,Ta)O${}_3$ (LSAT), and SrTiO${}_3$ (STO)] with (001) orientation. The physical properties of LaCoO${}_3$ films were characterized by the measurements of magnetic and transport properties. The LaCoO${}_3$ films undergo a paramagnetic to ferromagnetic (FM) transition at Curie temperatures ranging from 40 K to 85 K, below which the Pt/LCO hybrids exhibit significant extraordinary Hall resistance (EHR) up to 50 m$\mathrm{\Omega }$ and unconventional magnetoresistance (UCMR) ratio $\mathrm{\Delta }$$\rho$/${\rho }_0$ about $1.2\times {10}^{-4}$, accompanied by the conventional magnetoresistance (CMR). The observed spin transport properties share some common features as well as some unique characteristics when compared with well-studied Y${}_3$Fe${}_5$O${}_{12}$-based Pt thin films. Our findings call for new theories since the extraordinary Hall resistance and magnetoresistance cannot be consistently explained by the existing theories.