  The ultrathin film limit has been shown to be a rich playground for unusual
low dimensional physics. Taking the example of SrRuO$_3$ which is ferromagnetic
and metallic at the bulk limit, one finds that it becomes antiferromagnetic and
insulating at the three monolayers limit when grown on SrTiO$_3$. The origin of
the insulating state is traced to strongly orbital dependent exchange
splittings. A modest compressive strain of 1% of the SrTiO$_3$ substrate is
then found to drive the system into a highly confined two-dimensional 100% spin
polarized metallic state. This metal-insulator transition driven by a modest
strain could be useful in two state device applications.
