The frequency and field dependence of magnetic colloidal suspensions

Abstract

This thesis is a study of the dynamic magnetisation of various magnetic fluids, commonly known as ferrofluids. The fluids contain either magnetic nanoparticles, or magnetic microspheres. The method used to study the magnetization is the frequency and field dependent complex susceptibility, χ(ω, H) . Experimental data of χ(ω, H) is obtained using impedance measurement techniques. The slit toroid technique is used for measurement at frequencies below 10 MHz, whilst the transmission line technique is used for measuring at frequencies in excess of this. The impedance measurements are made by using a suitable impedance or network analyser, and are then inserted into a computer program which evaluates the susceptibility.