A stator core or a rotor core for an electrical machine, the core including a plurality of teeth separated by slots in a circumferential direction of the core, and a plurality of lamination stacks arranged one after another in an axial direction of the core, and separated from each other in the axial direction by cooling ducts. Each lamination stack includes at its each end in the axial direction at least one slit tooth section providing a discontinuity in the electrical conductivity of the lamination material and thereby reducing eddy current losses at the respective slit tooth section, and between the slit tooth sections at least one regular tooth section.