In this paper, the concept of double stators and the concept of magnetic gears are artfully integrated to form a novel class of machines. By utilizing the modulation-ring structure, the proposed machines can modulate the high-speed rotating armature field of the stators to match the low-speed rotating permanent-magnet (PM) field of the rotor. Hence, the machines readily achieve the low-speed high-torque merit. In addition, the fractional-slot structure can be adopted for the inner-stator design to remove the modulation-ring of the inner stator. Two possible machine structures are discussed and compared. Their characteristics and performances are calculated by using the time-stepping finite-element-method. The results well verify the validity of the proposed machine design.