The method of manufacturing a magnetic rotor unit comprises providing a composite magnetic rotor body. The composite magnetic rotor body comprises magnetic particles dispersed in a polymer resin. The composite magnetic rotor body has a hole. The method further comprises inserting a shaft into the hole. The outer diameter of the shaft corresponds to the inner diameter of the hole. The method further comprises heating of the shaft. By heating the shaft, the elevated temperature of the shaft surface preferentially induces the polymer resin from an inner surface of the hole to exude or sweat on to the shaft surface, so as to provide a bonding layer between the magnetic rotor body and the shaft. An apparatus for such manufacture, and a magnetic rotor unit manufactured by such method, are also provided. Such rotor units have wide application, and may for example be used in sensors, electromagnetic generators, pulse generators, motors, magnetic brakes and magnetic couplings.