Types of Stepper Motor:
Permanent magnet stepper
The permanent magnet stepper motor uses a permanent magnet (PM) as rotor, which operates on the attraction or repulsion to the stator electromagnets. The most important features of this motors are:
+ high torque
- Relatively big step angle
Variable reluctance (VR) stepper motor
Variable reluctance (VR) stepper motors have a rotor consisting of soft iron. This type of stepper motor operate based on the principle that minimum reluctance occurs with minimum gap. So the rotor endpoints are attracted toward the stator magnet poles.
+ Small price
+ Smaller step angles like the PM-stepper motor has are possible
Hybrid stepper motor
The hybrid stepper motor uses a permanent magnet with two separate soft iron rings as rotor at its poles.
+ small step angles are possible
+ maximum torque with a small package size
More information you get in this video.