  Epitaxial strain provides important pathways to control the magnetic and
electronic states in transition metal oxides. However, the large strain is
usually accompanied by a strong reduction of the oxygen vacancy formation
energy, which hinders the direct manipulation of their intrinsic properties.
Here using a post-deposition ozone annealing method, we obtained a series of
oxygen stoichiometric SrCoO3 thin films with the tensile strain up to 3.0%. We
observed a robust ferromagnetic ground state in all strained thin films, while
interestingly the tensile strain triggers a distinct metal to insulator
transition along with the increase of the tensile strain. The persistent
ferromagnetic state across the electrical transition therefore suggests that
the magnetic state is directly correlated with the localized electrons, rather
than the itinerant ones, which then calls for further investigation of the
intrinsic mechanism of this magnetic compound beyond the double-exchange
mechanism.
