No abstract

No abstract

No abstract

No abstract

No abstract

Measurements and analysis are presented of the incremental magnetic susceptibilities, χ∥(H0) and χ⊥(H0), of magnetic fluids subjected to an external polarizing field, H0. The technique of placing a fluid sample in a cylindrical coil positioned between the poles of a magnet and determining the susceptibility, at a fixed frequency, when the long axis of the sample is (1) parallel (χ∥(H0)) and (2) perpendicular (χ⊥(H0)), to H0, provides a convenient method for the determination of the magnetic moment, and hence the effective particle size, of nano-particles in magnetic fluids. Two magnetic fluids samples consisting of magnetite and cobalt-zinc ferrite particles, respectively, are investigated and the results obtained are found to be in good agreement with those of the manufacturer. As the samples are cylindrical in shape, the demagnetizing field, HD, for both the perpendicular and parallel orientations of the samples, is accounted for in calculating χ∥(H0) and χ⊥(H0).

A formula is derived for the complex, frequency-dependent, low-field relative susceptibility of a magnetic fluid which takes account of magnetic fluctuations of the intraparticle Neel-type and those induced by the rotational Brownian motion of the particles.

An alternative to the Cole-Cole method of analysing the distribution of relaxation times in ferrofluids together with some results for two colloidal suspensions of magnetite are reported.