Abstract: An electrical rotating machine having a stator or a rotor with a core that includes a plurality of tapered pole pieces is a low loss electrical machine that results in improvements such as higher output power, higher torque and higher efficiency than a machine that does not have tapered pole pieces. The stator or the rotor with tapered pole pieces may be applied to a power train in automobiles, power tools, and various appliances. The core is constructed by winding an iron-based amorphous magnetic alloy ribbon to form a cylinder-shaped core, then heating, impregnating with resin, and machining by cutting the cylinder-shaped core to form a plurality of tapered pole pieces being separated in an alternating manner by a plurality of slots. The cores having an outside diameter of 50 mm-1200 mm, a tapered angle of 10°-45°, and a slot depth of 10 mm-210 mm are advantageous.