An alternator for a vehicle comprises two pole pieces having interlaced poles (10) and magnets, the poles exhibiting grooves profiled along an axis (21) and accommodating the magnets, the profile completely preventing the magnets escaping from the grooves in a plane perpendicular to the axis (21).;It has, for each magnet (20), a strip (24) interposed between one face (25, 27) of the magnet and at least one of the grooves (18), the strip (24) being produced from a material which is less hard than the magnet.
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