NOVELTY - The assembly has a magnet arrangement (860a) comprising a first magnetic component part (1) and a second magnetic component part (2) that are attached to a mechanical support structure. The first magnetic component part and a second magnetic component part are arranged along an axial direction (Z) of the assembly, where a first cross section of the first magnetic component part includes a first shape with respect to the axial direction, and a second cross section of the second magnetic component part includes a second shape that is different from the first shape.    USE - Rotor assembly for an electromechanical transducer e.g. motor and synchronous electric generator, of a wind turbine (all claimed). Can also be used for an electric vehicle.    ADVANTAGE - The assembly shapes the magnet arrangement along axial direction cogging torque such that torque ripples of an electric machine equipped with the assembly is reduced in an easy and effective manner. The assembly allows a brake to be provided to stop operation of the wind turbine or to reduce rotational speed of the rotor for an emergency, for too strong wind conditions, which harm the wind turbine and for intentional saving of consumed fatigue life time and fatigue life time consumption rate of a structural component of the wind turbine. The assembly reduces skewing, so that efficiency for the electromechanical transducer is improved.    DETAILED DESCRIPTION - The first shape is a first geometrically irregular shape. The second shape is a second geometrically irregular shape. The first magnetic component part and the second magnetic component part are separate magnetic pieces.    DESCRIPTION OF DRAWING(S) - The drawing shows a perspective view of magnet arrangement including three respectively six magnetic component parts that are formed integrally by one magnet piece.    Circumferential direction (alpha)    Radial direction (r)    Axial direction (Z)    Magnetic component parts (1, 2, 3)    Magnet arrangement (860a)