Field-dependent phase diagram of the structural pattern in a ferrofluid film under perpendicular magnetic field

Abstract Influences of both the magnetic field strength H and the sweep rate d H /d t on the structural pattern evolution in a magnetic fluid film under perpendicular fields are systematically investigated. When the magnetic field is increased at a given rate, the structure evolves from a monodispersed state to a disordered one, then to the first-level ordered hexagonal structure, and finally to the second-level ordered structure through a transition state. With a higher d H /d t , the range of the applied magnetic field corresponding to the first-level ordered structure is widened and the field H s , at which the transition occurs becomes higher. An empirical power law H s ∝(d H /d t ) 0.4 was found. A phase diagram for the magnetic fluid film in the H –d H /d t plane is presented.