Reversible ordered agglomeration of hematite particles due to weak magnetic interactions

Hematite particles of cubic morphology (∼ 1.2μm in size) dispersed in aqueous solutions form ordered agglomerates under the influence of a weak magnetic field, as observed in a metallurgical microscope. The aggregates are loose and could be easily redispersed, by applying shear or ultrasound. The phenomenon is explained in terms of the interaction energy of the double layer and the magnetic attraction between hematite particles, resulting in a secondary minimum.