Electric motor

An electric motor used for example in a magnetic disk drive, comprises a rotor having a hub on which the magnetic disk is mounted, and an annular driving permanent magnet, and rotating together with a rotary shaft, and a stator disposed outside the rotor, having a core and coils wound on the core. A signaling permanent magnet for detecting the rotary angle or the rotational speed of the rotor may be provided on the radially inner side of the driving permanent magnet. Part of the outer periphery of the stator core may be retracted radially inward or cut away to form a concavity or an open part. A magnetic shielding plate may further be provided to cover the coils, with part or the entirety of the magnetic shielding plate being positioned closer to the rotary shaft than the outermost periphery of the rotor to prevent the escape of the rotor in the direction of the rotary shaft. The stator core may be provided, at its inner extremities, bent portions extending in the direction parallel with the rotary shaft, and away from the hub. Alternatively, the midpoint of the stator core may be positioned farther away from the hub than the midpoint of the driving permanent magnet.