  Pure rutile Co-doped TiO$_2$ films were fabricated successfully by the
conventional pulsed laser deposition technique on silicon substrates from a
ceramic target. Under the right fabrication conditions, Co concentration in the
films could be almost the same as in the synthesized target, and films under
various conditions all are ferromagnetic well above room temperature. Even
though Rutherford backscattering spectroscopy measurements show that Co atoms
seem to be mostly localized near the surface of the films and less exist in
deeper levels, other experimental evidences show that the ferromagnetism does
not come from Co segregations but from the Co-doped TiO$_2$ matrix. Rutile
Ti$_1-x$Co$_x$O$_2$ thin films grown by a very simple technique on low-price
silicon substrates showing Curie temperature (TC) above 400 K appear to be very
attractive to applications.
