Evidence of second order phase transition of ferrofluid in external electric field.

When a DC electric field is applied perpendicular to a thin film of ferrofluid constrained between two conducting plates, the ferrofluid separates into phases that are concentrated and dilute in magnetic particles for field strength above a critical value. The phase separation stems from the competition between the electrostatic energy and entropy of the induced dipoles. The entropy around the critical value of the phase separation is continues in our experiment indicating the transition is second order.