in a method of magnetizing a cylindrical body comprising a substantially isotropically distributed material according to the present invention , the method comprises the steps of : applying a magnetic field to the body ; and varying the magnetic field circumferentially around the body thereby to achieve at least over a part of the cylinder a generally sinusoidal magnetization circumferentially . thus , can advantageously be achieved a sinusoidal flux density distribution for , in particular , rotors for electric motors in the air gap surrounding the rotor . the resultant sinusoidal back - emf waveform is ideal for high precision servo applications . in addition , when a high pole number is adopted , such bodies can be mounted on air cored rotor - hubs , which enable a substantial reduction in inertia , without substantial loss of performance .