Characteristics of magnetic materials

Magnetic materials have magnetically ordered strong magnetic substances, and broadly include weak magnetic and antiferromagnetic substances that can apply their magnetism and magnetic effects.

Magnetism is a basic property of matter. Substances can be divided into diamagnetic, paramagnetic, ferromagnetic, antiferromagnetic and ferrimagnetic substances according to their internal structure and their properties in external magnetic fields.

Ferromagnetic and ferrimagnetic substances are strong magnetic substances, and diamagnetic and paramagnetic substances are weak magnetic substances.

Magnetic materials are divided into two types according to their properties: metallic and non-metallic. The former mainly include electrical steel, nickel-based alloys and rare-earth alloys, and the latter are mainly ferrite materials.

　　 Magnetic material characteristics:

　　 ① Even if there is no external magnetic field, there are still permanent magnetic moments in small areas (magnetic domains) inside the material. However, the direction of the magnetic moment of each magnetic domain is arbitrarily distributed when the unmagnetized magnetic material has no external magnetic field, and the vector sum is zero, so the entire material has no magnetic properties.

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

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

　　④Hysteresis exists. That is, the change of magnetic induction lags behind the change of magnetic field.