  Ferrofluids currently are the only type of magnetic liquid materials with
wide practical use. The theory on ferrofluids is an example of success to apply
statistics to science. Ferrofluids are two-phase liquids consisting of
dispersed nanoscale ferromagnetic particles suspended in a carrier fluid. Due
to their tiny size, individual ferromagnetic particles clearly exhibit Brownian
motions. Only when a large number of randomly-moving particles are subject to
an external magnetic field, can they collectively exhibit magnetization at a
macroscale. Using statistical theory, the magnetization of a ferrofluid can be
characterized by the celebrated Langevin equation. The monograph combines
statistical theory and the method of Dirac function to establish equations for
ferrofluids under several conditions, including magnetization relaxation,
magnetization equilibrium, and magnetization freezing. It thus provides a quite
complete account of the theory of ferrofluid dynamics.
