  The Gaussian Effective Potential (GEP) is shown to be a useful variational
tool for the study of the magnetic properties of strongly correlated electronic
systems. The GEP is derived for a single band Hubbard model on a
two-dimensional bi-partite square lattice in the strong coupling regime. At
half-filling the antiferromagnetic order parameter emerges as the minimum of
the effective potential with an accuracy which improves over RPA calculations
and is very close to that achieved by Monte Carlo simulations. Extensions to
other magnetic systems are discussed.
