Magnetic materials Materials with ferromagnetic properties have the following characteristics:

(1) Even if there is no external magnetic field, there is still a permanent magnetic moment in various small regions (magnetic domains) inside the material. However, when there is no external magnetic field, the magnetic moment direction of each magnetic domain is arbitrarily distributed, and its vector sum is zero, so the material as a whole is not magnetic.

(2) Easy magnetization. This is because under the action of the external magnetic field, the magnetic moment direction of each magnetic domain is turned to the direction of the magnetic field, so a large magnetic induction intensity B can be obtained. According to the formula B = μrB0 (B0 is the magnetic induction intensity in a vacuum), the relative permeability μr of the magnetic material is very large. In fact, the μr of magnetic materials reaches 10~10, while the μr of non-magnetic materials ≈1.

(3) There is a magnetic saturation phenomenon, that is, B increases with the increase of H, but after increasing to a certain value of Bs, it no longer increases with H. BS is the saturation magnetic induction strength of the magnetic material. The reason for the saturation phenomenon is because the magnetic moment of all magnetic domains turns to the direction of the magnetic field after H reaches a certain value. For this reason, B and H are not linear, so the magnetic permeability is not constant, but related to the strength of the magnetic field.

(4) There is hysteresis. That is, the change in the intensity of magnetic induction lags behind the change in the magnetic field.