  We propose a controllable method for observing interaction induced
ferromagnetism in ultracold fermionic atoms loaded in optical superlattices. We
first discuss how to probe and control Nagaoka ferromagnetism in an array of
isolated plaquettes (four lattice sites arranged in a square). Next, we show
that introducing a weak interplaquette coupling destroys the ferromagnetic
correlations. To overcome this instability we propose to mediate long-range
ferromagnetic correlations among the plaquettes via double-exchange processes.
Conditions for experimental realization and techniques to detect such states
are discussed.
