Coercive force is the value of the external magnetic field that brings to zero the magnetization or magnetic flux density of a magnetic body. The external magnetic field is oriented in the opposite direction from the orientation of the of the magnetic body itself. The value of the external magnetic field when the magnetic polarization (or magnetization) and magnetic flux density of the magnetic body come to zero are written as HcJ and HcB to distinguish them, but when evaluating magnetic characteristics, normally the coercive force is expressed as HcJ. Coercive force is a measure of the stability of magnetization in the face of an external magnetic field or more simply the capacity to resist an external magnetic field. Material with high coercive force is called hard magnetic material and material with low coercive force is known as soft magnetic material. This is the most important characteristic for a permanent magnet material.