The invention relates to a rotor (1) of an electromagnetic motor or generator having a body comprising an inner hub (2) which is concentric to a central axis (7) of rotation of the rotor (1), branches (3) extending radially with respect to the central axis (7) of rotation from the inner hub (2) towards a hoop (8) forming a circular outer periphery of the rotor (1), at least one magnet (10) being housed in each space delimited between two adjacent branches (3), each having a width which decreases with distance from the inner hub (2) and terminates by a tapered tip (3b) against the hoop (8). Each magnet is in the form of a magnet structure (10) consisting of a plurality of individual magnets (4) which are secured together by a fiber-reinforced insulating material, each individual magnet (4) being elongated in shape by extending in the axial direction of the rotor (1).