  In this paper we report universal labyrinthine patterns observed in
nanocolloids originated from electric-field-induced phase separation. For
nanocolloids consisting of magnetic particles (magnetic fluids), the
labyrinthine pattern as the result of the co-existence of two phases is found
to be stable against perturbation by an additional magnetic field. The
relaxation back to the globally disordered pattern after the magnetic field is
removed clearly shows evolution of "undulation" thus demonstrates that
superimposing magnetic and electric fields can easily manipulate the patterns
resulted from the phase separation, indicating that a magnetic fluid has an
advantage in exploring the dynamics of defects that has applications in many
fields.
