High-spin polarized Co-doped (La,Sr)TiO₃ thin films on high-mobility SrTiO₃ substrates

We report on the magnetotransport properties and spin polarization of Co-doped (La,Sr)TiO₃ (Co-LSTO) thin films in which the host oxide is a strongly correlated metal with a high density of carriers. In order to probe the spin polarization, we have performed tunneling magnetoresistance (TMR) measurements on magnetic tunnel junctions associating Co-LSTO and Co electrodes. A large spin polarization of around -80% has been determined at low temperatures, indicating that the carriers in this system are highly spin-polarized. We also report on the planar magnetotransport experiments on Co-LSTO films grown on SrTiO₃ substrates. The electrical properties of these samples are strongly dependent on the growth conditions and large electronic mobilities as high as 10⁴ cm²/V s at T<10 K are observed for specimens grown at the lowest oxygen pressure. We show that this high-mobility state is three-dimensional and we relate it to the doping of the SrTiO₃ substrate with oxygen vacancies.