The main magnetic properties of permanent magnet materials are: remanence (Jr, Br), coercivity (Hcb), intrinsic coercivity (Hcj), and magnetic energy product (BH) max. The magnetic properties of the permanent magnet materials we usually refer to are the four items. Other magnetic properties of permanent magnet materials include: Curie temperature (Tc), operating temperature (Tw), reversible temperature coefficient of remanent magnetism and intrinsic coercivity (α, β), and reductive permeability (μrec) demagnetization curve. Squareness (Hk/Hcj), high-temperature demagnetization performance, and uniformity of magnetic properties.

　　In addition to magnetic properties, the physical properties of permanent magnet materials include density, electrical conductivity, thermal conductivity, thermal expansion coefficient, etc. Mechanical properties include Vickers hardness, compressive strength, impact toughness and so on. In addition, an important one of the performance indicators of permanent magnet materials is the surface state and its corrosion resistance.

　　The main raw materials of Nd-Fe-B magnets are rare earth metal neodymium, metal element iron and nonmetallic element boron (sometimes adding aluminum, cobalt, praseodymium, dysprosium, terbium, gallium, etc.), the general expression is Re2TM14B (RE=Nd, Pr, Dy TM=Fe, Co).

　　NdFeB magnet three component permanent magnet material is made of Nd2Fe14B compound, and its composition should be similar to that of Nd2Fe14B compound. However, when the ratio of Nd2Fe14B is completely distributed, the magnetic properties of the magnet are very low or even non-magnetic. It is only in the actual magnets that the content of Nd and B is more than the content of Nd and B of the Nd2Fe14B compound (i.e. the formation of neodymium rich phase and boron rich phase) can obtain better permanent magnetic properties.

　　Matrix Nd2Fe14 phase

　　The phase is the main phase of the magnet, the percentage of its volume (which is basically fixed after the ingot is finished) determines the remanence (Br), the maximum magnetic energy product ((BH) m) of the magnet, and the orientation of the magnetic field is to realize its arrangement and distribution so that the magnetized axis (C) of this molecular structure is arranged in an orderly direction in order to achieve a higher magnetic energy. .

　　Rich B phase

　　The rich B phase exists in the matrix with a certain compound. It is a nonmagnetic phase and is generally harmful to the magnetic energy, but it is easy to break the ingot with the existence of the rich B phase.

　　Generally, sintered NdFeB permanent magnets are selected according to different use environments. Generally, sintered NdFeB, which is considered to have suction requirements, is concentrated in N and M files, and requires high magnetic energy product. Most of the sintered NdFeB permanent magnets that consider the irreversible requirements of magnetic flux are concentrated in the H, SH, UH, and EH grades, and their sizes are usually related to magnet composition, magnetic properties, size, and test methods. Sintered NdFeB permanent magnets with corrosion resistance requirements are related to the surface treatment type and process of the magnet, such as electroplating Zn, Ni, NiCuNi, black epoxy and NiCu epoxy.

　　The magnetic circuit is composed of one or more permanent magnets, current carrying wires and soft iron according to a certain shape and size to form a component with specific working air gap magnetic field. Soft iron can be pure iron, low carbon steel, Ni-Fe, Ni-Co alloy and other materials with high permeability. Soft iron, also known as yoke iron, plays a role in controlling magnetic flux direction, increasing local magnetic induction intensity, preventing or reducing magnetic flux leakage, and improving the mechanical strength of the whole component.

　　Generally, the magnetic state in which a single magnet is located without soft iron is referred to as an open state; when the magnet is in a magnetic flux loop formed by a soft iron, the magnet is said to be in a closed state

　　Ferromagnetic materials can be used to shield magnetic fields. Generally, we use ordinary iron plates. However, it is necessary to pay attention to the thickness of the iron plate. If the thickness is not reached, the iron plate is in the state of magnetic saturation, only a partial magnetic field can be shielded, and some of the magnetic lines of force will still be diverged. The key to guide magnetic field to form magnetic circuit is to select high magnetic material and suitable size and shape to reduce magnetic flux leakage.