Characteristics of magnetic materials

Magnetic materials are strong magnetic substances with magnetic ordering, and broadly include weak magnetic and antiferromagnetic substances that can be applied to their magnetism and magnetic effects.

Magnetism is a fundamental property of matter. Substances can be classified into diamagnetic, paramagnetic, ferromagnetic, antiferromagnetic, and ferrimagnetic substances based on their internal structure and properties in an external magnetic field.

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

Magnetic materials are divided into two categories based on their properties: metallic and non-metallic. The former mainly includes electrical steel, nickel based alloys, and rare earth alloys, while the latter mainly consists of ferrite materials.

Magnetic material properties:

① Even without an external magnetic field, permanent magnetic moments still exist in various small regions (magnetic domains) inside the material. However, in the absence of an external magnetic field, the magnetic moment direction of each magnetic domain in an unmagnetized magnetic material is arbitrarily distributed, and its vector sum is zero, so the material as a whole has no magnetism.

② Easy to magnetize. This is because under the action of an external magnetic field, the magnetic moment direction of each magnetic domain tries to rotate towards the direction of the magnetic field, resulting in a large magnetic induction intensity B. According to the formula B=μ rB0 (B0 is the magnetic induction intensity in vacuum), the relative permeability μ r of magnetic materials is very high. In fact, the μ r of magnetic materials reaches 10-10, while the μ r of non-magnetic materials is ≈ 1.

③ There is a phenomenon of magnetic saturation, where B increases with the increase of H, but after reaching a certain value 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 that after H reaches a certain value, the magnetic moments of all magnetic domains turn towards the direction of the magnetic field. Due to this reason, B and H do not have a linear relationship, and therefore the magnetic permeability is not a constant, but is related to the magnetic field strength.

④ There is hysteresis phenomenon. The change in magnetic induction intensity lags behind the change in magnetic field.