One is to replace the rotor magnet with a solid iron rotor and use the iron's ferromagnetic property to generate torque.
(One; is; to replace the rotor magnet with a solid iron rotor and use the iron's ferromagnetic property to generate torque) (One; to use; the iron's ferromagnetic property; to generate torque)
One One
is to use
to replace the rotor magnet with a solid iron rotor and use the iron's ferromagnetic property to generate torque
the iron's ferromagnetic property to generate torque