Micro-structures and potentially electro-optic applications of magnetic fluid films

Summary form only given. Under external magnetic fields, a variety of structural patterns of chains/columns in the ferrofluid thin film have been observed. Under the action of externally-applied magnetic fields, a portion of magnetic particles was condensed out from the initially monodispersed magnetic fluid and formed into magnetic chains/columns. These chains/columns evolved from a disordered phase to an ordered structural pattern as the field strength reached some critical value, H/sub c/, which is dependent on several controllable parameters, such as field strength, sweep rate, volume concentration, thickness of film, temperature, and direction of field. It was further discovered that the optical transmittance of magnetic fluid films can be controlled by these parameters and is directly affected by the volume of the condensed particles. Moreover, for the ordered structures, the characteristic spacing in the structure pattern can be manipulated within a range from submicrometers to tens of micrometers by adjusting the controllable parameters. The ordered structures generate magnetochromatic and the magneto-optic effects, such as birefringence, field-dependent transmittance, etc., for the ferrofluid thin films. These phenomena bring up the promising possibility of fabricating electro-optic devices, e.g. optical switch, filter, grating, or even photonic-crystal waveguide and cavity, by using homogeneous ferrofluid films.