Ferromagnetic Particles are prepared using chromium dioxide coated onto uniform polystyrene particles. These particles retain magnetism once exposed to a magnetic field. The particles can be demagnetized and re-magnetized repeatedly and reproducibly. Ferromagnetic particles have been used for studying mechanotransduction across the cell surface and through the cytoskeleton by binding ferromagnetic particles to cell surface receptors and applying mechanical stress directly to the receptor using a device to twist the magnetic particle on the cell surface.