Negative spin polarization in Co$\vert $SrTiO$_{3}$$\vert $Co magnetic tunnel junctions$^{1}$

We perform an \textit{ab-initio }study of spin-polarized tunneling in epitaxial Co\textit{$\vert $}SrTiO$_{3}$\textit{$\vert $}Co magnetic tunnel junctions with bcc Co(001) electrodes. We predict a large tunneling magnetoresistance in these junctions, originating from a mismatch in the majority- and minority-spin bands both in bulk bcc Co and at the Co\textit{$\vert $}SrTiO$_{3}$ interface. The intricate complex band structure of SrTiO$_{3}$ enables effcient tunneling of the minority $d$-electrons which causes the spin polarization of the Co\textit{$\vert $}SrTiO$_{3}$ interface to be negative in agreement with experimental data$^{2}$. Our results indicate that epitaxial Co\textit{$\vert $}SrTiO$_{3}$\textit{$\vert $}Co MTJs with bcc Co(001) electrodes is a viable alternative for device applications. [1] J. Velev et al., Phys. Rev. Lett. \textbf{95}, 216601(2005). [2] J. M. De Teresa \textit{et al.}, Phys. Rev. Lett. \textbf{82}, 4288 (1999); J. M. De Teresa, \textit{et al.}, Science \textbf{286}, 507 (1999).