Effect of a Demagnetizing Field (Self-Demagnetizing)
This internal magnetic field is called a demagnetizing field, and works to demagnetize the magnet. This demagnetizing field differs according to the magnet’s proportions, and it becomes smaller as the magnet gets longer and narrower in the magnetizing direction.
Permeance Modulus
The effect of the demagnetizing field is practically shown by the slope of Bd/Hd, as the ratio between the magnetic flux field and demagnetizing field. This P=Bd/Hd is called “permeance modulus”, the straight line of the permeance modulus is called the “operating line”, and the intersection point with the demagnetizing curve is called the operating point.