  We demonstrate the stability of ferromagnetic order of one unit cell thick
optimally doped manganite (La0.7Ba0.3MnO3, LBMO) epitaxially grown between two
layers of SrRuO3 (SRO) by using x-ray magnetic circular dichroism. At low
temperature LBMO shows an inverted hysteresis loop due to the strong
antiferromagnetic coupling to SRO. Moreover, above SRO TC the manganite still
exhibits magnetic remanence. Density Functional Theory calculations show that
coherent interfaces of LBMO with SRO hinder electronic confinement and the
strong magnetic coupling enables the increase of the LBMO TC. From the
structural point of view, interfacing with SRO enables LBMO to have octahedral
rotations similar to bulk. All these factors jointly contribute for stable
ferromagnetism up to 130 K for a one unit cell LBMO film.
