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$\Omega$ and unconventional magnetoresistance (UCMR) ratio $\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.