An interior permanent magnet rotor, for a drive unit disposed in the interior of a hermetically sealed housing of a refrigerant compressor, whereas the rotor includes a first axial section with permanent magnets, followed by a second axial section without permanent magnets. In order to reduce the risk of a magnetic short-circuit it is provided that the second axial section, adjacent to the first axial section, includes a first axial subsection with a reduced radial dimension not going beyond the permanent magnets in the first axial section, whereas the axial length of the first axial subsection is smaller than the axial length of the first axial section, and the second axial section, adjacent to its first axial subsection, includes a second axial subsection with a radial dimension larger than the reduced radial dimension of the first axial subsection.