What is claimed is:1. An interior permanent-magnet motor comprising: a stator having a coil wound therearound, and a rotor rotatably disposed inside of the stator, whereinthe rotor includes a rotor core that is a laminate of a plurality of pieces of metal foil made of a soft magnetic material that are stacked in a direction of a rotation axis of the rotor,the rotor core has a plurality of through-holes that penetrates through the rotor core in the direction of the rotation axis, the plurality of through-holes including through-holes embedding magnets,the rotor core has inner bridges and outer bridges, the inner bridges extending between the through-holes that are adjacent to each other, the outer bridges being located between the through-holes close to an outer circumference of the rotor core and the outer circumference of the rotor core, andat least one of the inner bridges and the outer bridges in the rotor core includes an amorphous soft magnetic material, and the other parts of the rotor core include a nanocrystal soft magnetic material.2. The interior permanent-magnet motor according to claim 1, wherein the outer bridges include an amorphous soft magnetic material.3. A method for manufacturing an interior permanent-magnet motor including: a stator having a coil wound therearound, and a rotor rotatably disposed inside of the stator, the method comprising:preparing metal foil pieces each made of an amorphous soft magnetic material and having a shape corresponding to a shape of a rotor core of the rotor, the metal foil piece having a plurality of through holes including through-holes to embed magnets;selecting at least one of inner bridges and outer bridges from each of the prepared metal foil pieces, the inner bridges extending between the through-holes that are adjacent to each other, the outer bridges being located between the through-holes close to an outer circumference of the metal foil piece and the outer circumference of the metal foil piece, and heating parts other than the selected bridges to alter the heated parts from the amorphous soft magnetic material to a nanocrystal soft magnetic material while keeping the selected bridges as the amorphous soft magnetic material; andstacking the altered metal foil pieces in a direction of a rotation axis of the rotor, and embedding magnets in the corresponding through-holes to manufacture the rotor core.4. The method for manufacturing an interior permanent-magnet motor according to claim 3, wherein the selected bridges for altering include the outer bridges.5. The interior permanent-magnet motor according to claim 1, wherein the nanocrystal soft magnetic material has a crystallite diameter that is less than 1 μm.6. The method for manufacturing an interior permanent-magnet motor according to claim 3, wherein the nanocrystal soft magnetic material has a crystallite diameter that is less than 1 μm.
