A composite paramagnetic particle and method of making are provided. In one aspect of the invention, a particle comprising a multitude of submicron polymer bead aggregates covalently cross-linked to each other to form larger diameter particles is presented. Distributed throughout the composite paramagnetic particle are vacuous cavities. Each submicron polymer bead has distributed throughout its interior and surface submicron magnetite crystals. In another aspect of the invention, composite particles are made using high energy ultrasound during polymerization of one or more vinyl monomers. In one embodiment, high energy ultrasound is used during an emulsification step and during the early stages of the polymerization process to produce micron sized composite paramagnetic particles. The particles according to the invention exhibit a high percent magnetite incorporation and water and organic solvent stability.