7.7. FERROFLUIDS
187
Figure 7.22. Maggnetization curve for a ferrafluid made of magnetite. F%O,. nanoparticles
showing the soft (nonhyslerelic) magnetic behavior. An oersted corresponds to
T fAdapted
lrom D. K Kim, J. M q n . M a p . Mater, 225. 30 (2001).]
Analopous prepflies are observed in liquid ctystaIs, which Consist of long
molecules having large electric dipole moments, which can hc oricnktl hy the application of an electric field in the fluid phase. Electric-field-niodulntcd birefringencc
or doublc rehction of liquid crystals is widely used in optical dcviccs, such as
liquid crysral displays in digital watches, and screens of portnhlc computers. This
siiggcs&i a potential application o f ferrofluids employing magnetic Iicld induced
hifirngcficc. To observe the behavior, the ferrofluid is sealed in a glnss ccll having a
thickness of several micrometers. When a DC magnetic field is applinl pnrallel to
Bgure 7.23. Picture taken through an optical microscope of chains of magnetic nanoparticles
formed m a film of a Ferrofluid when the DC magnelic fteld IS parallel to the plane 01 the film [With
permission lrom H. E. Hornig et al., J, fhys. Chem. Sol& 62, 1749 (2WI).]