Magnetic spectroscopy as a tool in characterizing magnetic fluids
Pages 1-8
P. C. Fannin
Abstract. There is an ever increasing interest in magnetic fluids which now find applications in a variety of diverse areas ranging from magnetic seals, to drug targeting and in the treatment of hypertermia. Thus it is important to be able to accurately characterise such fluids and one means is by the measurement of the frequency dependent, complex susceptibility, ()χω. From measurement of()χω at frequencies below 1GHz, relaxation mechanisms both Brownian and Néel, can be investigated and identified. This data, in conjunction with the Debye equations enables the average particle hydrodynamic or magnetic radius to be determined. As the frequency is increased to the GHz region, a point is reached where the character of the dispersion changes from relaxation to one of resonance. Data from this region provides a convenient means of investigating further properties of the fluids, such as the effective particle anisptropy constant K, and the gyromagnetic constant, γ, the exponential prefactor, 0τ, of the Neel expression for Nτ and indeed Nτ itself.