The temperature dependence of magnetization in ferrofluids

Ferrofluid samples were prepared for magnetic characterization prior to use in a ESA experiment on convection currents in microgravity conditions on the International Space Station. The experiment requires a fluid with a highly temperature dependent magnetization at low field over the temperature range of 30–100°C. Ni–Zn ferrites of varying chemical composition were prepared in order to investigate the effect of a change in the Curie temperature on the temperature dependence of magnetization. Ni0.5Zn0.5 was found to be the composition with the largest ΔM of 0.4emu∕g. Magnetite samples were prepared to investigate the effect of high MS and varying particle size on ΔM. Magnetite fluids with particle sizes of 6 and 10nm have ΔM’s of 0.8 and 1.6emu∕g, respectively. Therefore, the dominant effect is high MS and particle size driven by the field dependence of the Langevin function.