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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.

We report on magnetisation reversal processes in metal particle (MP) pigments and tapes which are the standard for all advanced data storage formats on flexible substrates. In addition to describing the basis of the technology and the principles of the preparation process, we describe the origin of the magnetic properties and how these are controlled to meet the specifications for advanced storage formats. Critical to the application of any material as a data storage medium is the switching field distribution (SFD) which is controlled by the particle size distribution (PSD), the magnetic anisotropy (K), the magnetisation reversal mechanism of the particles and particularly the alignment of the particle easy axes on the tape. We describe how each of these parameters in turn is measured and how control of the parameters is achieved. In particular, we find that close control of the PSD and particularly the particle orientation controls the effective SFD. In the most advanced systems the SFD is dominated by the alignment of the particles, which means that control of the particle morphology is required to obtain a high degree of easy axis alignment. In this regard we also describe new developments in MP technology and look to prospects for further advances.