Shape Distribution of Magnetic Powders

In work reported earlier, the average length-to-diameter ratios determined magnetically did not agree with those observed under the electron microscope; this was thought due to magnetic interactions. This paper describes further shape determination measurements on γ-Fe2O3 samples of increasing dilution by the original method and by two analogous methods described by Wohlfarth. The results show a slight increase of mean length-to-diameter ratio with dilution and a considerable broadening of the distribution toward large length-to-diameter ratios. The different methods of measurement described do not yield the expected congruent curves at very low concentration. This indicates a deviation from Stoner-Wohlfarth rotation in these particles. The details of the mathematical methods are also described.