Inverse tunnel magnetoresistance in all-perovskite junctions of ${\mathrm{La}}_{0.7}{\mathrm{Sr}}_{0.3}{\mathrm{MnO}}_3/{\mathrm{SrTiO}}_3/{\mathrm{SrRuO}}_3$

All epitaxial oxide magnetic tunnel junctions, ${\mathrm{La}}_{0.7}{\mathrm{Sr}}_{0.3}{\mathrm{MnO}}_3/{\mathrm{SrTiO}}_3/{\mathrm{SrRuO}}_3$ trilayer films, composed of ferromagnetic and metallic electrodes were fabricated on STO(001) substrates. Inverse tunnel magnetoresistance (TMR), i.e., higher and lower junction resistance levels in parallel and anti-parallel magnetization configurations, respectively, was observed, indicating the negative spin polarization of ${\mathrm{SrRuO}}_3$ in contrast to the positive one of ${\mathrm{La}}_{0.7}{\mathrm{Sr}}_{0.3}{\mathrm{MnO}}_3.$ The TMR action persists up to $T_{\mathrm{C}}$ of the ${\mathrm{SrRuO}}_3$ layer due to the robust spin polarization at the ${\mathrm{SrTiO}}_3/{\mathrm{SrRuO}}_3$ interface.