Hysteresis properties of sized dispersed monoclinic pyrrhotite grains

Monoclinic pyrrhotite (Fe 7 S 8 with 4C superstructure) was magnetically separated from a massive pyrrhotitic ore for preparation of nine grain‐size fractions ranging from ∼ 80 µm (large multidomain grains) to < 3 µm (single‐domain grains). Grains smaller than 100 µm were found to be magnetically hard with coercive forces ranging from 135 oe for 83 µ grains to 920 oe for < 3 µm grains. For grain sizes between 83 µm and 7 µm the coercive force is given by H c ⧜ d −0.79 . Variations in hysteresis properties with grain size appear to be gradual, with no evidence of sudden changes associated with domain structure transitions.