X-ray microtomography of field-induced macro-structures in a ferrofluid

Abstract X-ray microtomography is used to visualize, in-situ, the three-dimensional nature of the magnetic field induced macro-structures (>1 μm) inside a bulk (∼1 mm diameter) magnetite-particle–mineral oil ferrofluid sample. Columnar structures of ∼10 μm diameter were seen under a 0.35 kG applied magnetic field, while labyrinth type structures ∼4 μm in width were seen at 0.55 kG. The structures have height/width aspect ratios >100. The results show that the magnetite volume fraction is not constant within the structures and on average is considerably less than a random sphere packing model.