A rotor apparatus for a permanent-magnet motor has the main technical feature of a ring rotor with its magnets arranged according to the Halback magnetic ring array. In addition, for a distance between magnets of a parallel array and the outer ring edge of the rotor, and for a diameter difference between the inner and outer diameters of the ring rotor, a ratio between said distance/said diameter difference is between 0.43 and 0.48.