Rotor temperature rise has not attracted enough attention during the designing of initial low power permanent magnet synchronous motors (PMSMs). Slot effect of stator windings, magnetomotive force of non-sine windings, and harmonic electrodynamic force generated by harmonic current will all cause eddy current losses in the rotor magnets and rotor yoke. Rotor eddy current loss is relatively small in comparison with stator’s copper loss and iron loss. With the increase in motor power, rotation speed, and permanent magnet’s volume, eddy current in permanent magnets will result in the higher temperature rise, then lead to the demagnetization and decrease motor performance. Lifetime of permanent magnets in the rare earth permanent magnet motor is largely determined by electrical resistivity, but those magnets are always have high conductivity and low heat resistance. Samarium Cobalt SmCo magnets still have matchless high temperature performance and stability compared with Neodymium magnets. Laminated magnets are proven to reduce eddy current losses in high efficiency motors besides some conventional solutions, then the combination of SmCo magnets and magnet segmentation technology, laminated SmCo magnets, undoubtedly become the preferred choice for high temperature rotating machinery.