  We report the observation of the transition from an ordered solid-like phase
to a disordered liquid-like phase of a lattice of spikes on a ferrofluid
surface submitted to horizontal sinusoidal vibrations. The melting transition
occurs for a critical spike displacement which is experimentally found to
follow the Lindemann criterion, for two different lattice topologies (hexagonal
and square) and over a wide range of lattice wavelengths. An intermediate
hexatic-like phase between the solid and isotropic liquid phases is also
observed and characterized by standard correlation functions. This dissipative
out-of-equilibrium system exhibits strong similarities with 2D melting in
solid-state physics.
