  We present a study of the thickness dependence of magnetism and electrical
conductivity in ultra thin La0.67Sr0.33MnO3 films grown on SrTiO3 (110)
substrates. We found a critical thickness of 10 unit cells below which the
conductivity of the films disappeared and simultaneously the Curie temperature
(TC) increased, indicating a magnetic insulating phase at room temperature.
These samples have a TC of about 560 K with a significant saturation
magnetization of 1.2 +- 0.2 muB/Mn. The canted antiferromagnetic insulating
phase in ultra thin films of n< 10 coincides with the occurrence of a higher
symmetry structural phase with a different oxygen octahedra rotation pattern.
Such a strain engineered phase is an interesting candidate for an insulating
tunneling barrier in room temperature spin polarized tunneling devices.
