Magnetite domain state

An alternative way of identifying the domain state of magnetite utilizes the dependence of both the crystal and strain anisotropy constants on temperature. Kj of eq. (7.2) is negative at RTand becomes positive at -118 K, which is the so-called Ver-wey transition at which the crystal anisotropy vanishes and any original remanence, which is controlled by this anisotropy, is lost. This provides an easy test for the do-... 

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. 

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