Domains, magnetic stability

The magnetite particles so produced were stabilized by protective colloids such as gelatin for use in magnetic domain observations. These precipitated magnetite particles are used for production of magnetic fluids, as we describe later. 

Coercivity and saturation magnetisation parameters are influenced by domain state (and hence by grain size of the magnetic fraction). Domain state in materials where the remanence is dominated by magnetite can be determined by position on a Day plot (Day et al., 1977) on such a plot, stability of remanence increases towards the upper left comer. Samples BC4, RC2, RC3, and RC5, all of which show evidence in their demagnetisation behaviour for the presence of a reversed-polarity component, plot closest to the stable part of the Day plot (Fig. 10). Samples BCl, BC3, BC5, and RCl 1, which do not show a clearly isolated reversed component, plot in less stable positions. Samples RC4 and RCl2, which have complex demagnetisation, plot as outliers, well to the less stable side of the plot. 

A brief explanation of the mechanism of hysteresis in a ferromagnetic substance follows. When a ferromagnetic substance is placed in a magnetic field, magnetic domains that are parallel to the applied field are stabilized. On the other hand, magnetic domains that are anti-parallel to the field are destabilized, and the stable domain expands, as shown in Fig. 10b. Although a... 

---