  Low-dimensional quantum materials that remain strongly ferromagnetic down to
mono layer thickness are highly desired for spintronic applications. Although
oxide materials are important candidates for next generation of spintronic,
ferromagnetism decays severely when the thickness is scaled to the nano meter
regime, leading to deterioration of device performance. Here we report a
methodology for maintaining strong ferromagnetism in insulating LaCoO3 (LCO)
layers down to the thickness of a single unit cell. We find that the magnetic
and electronic states of LCO are linked intimately to the structural parameters
of adjacent "breathing lattice" SrCuO2 (SCO). As the dimensionality of SCO is
reduced, the lattice constant elongates over 10% along the growth direction,
leading to a significant distortion of the CoO6 octahedra, and promoting a
higher spin state and long-range spin ordering. For atomically thin LCO layers,
we observe surprisingly large magnetic moment (0.5 uB/Co) and Curie temperature
(75 K), values larger than previously reported for any mono layer oxide. Our
results demonstrate a strategy for creating ultra thin ferromagnetic oxides by
exploiting atomic hetero interface engineering,confinement-driven structural
transformation, and spin-lattice entanglement in strongly correlated materials.
