We present an optimization design of a slotless permanent-magnet brushless dc motor (400 W, 6000 rpm), with two-segment Halbach arrays. The optimization is based on a motor analytical model which is obtained by solving the magnetic scalar potential using the Fourier series. We show that the iron-cored Halbach configuration is better than the classical one and that the air-cored Halbach configuration is even better. This means that the rotor iron can be completely omitted. We verify the results by using the finite-element method.