The magnet is magnetized to saturation by an external magnetic field in a closed circuit state and then the external magnetic field is removed. The magnetic polarization intensity J and internal magnetic induction intensity B of the magnet do not disappear due to the disappearance of the external magnetic field H. Instead, they maintain a certain value, which is called the residual magnetic induction intensity of the magnet, abbreviated as residual magnetic Br. SI units are T, and CGS units are Gs (1T=104Gs)....

When a magnetic field H is applied to any medium, the magnetic field strength inside the medium is not equal to H, but rather manifested as the sum of H and the magnetic polarization strength J of the magnetic medium. Due to the fact that the magnetic field intensity inside the medium is manifested by the induction of the magnetic field H through the medium, it is called the magnetic induction intensity of the medium to distinguish it from H.

Modern magnetic research shows that all magnetic phenomena originate from electric currents, and a unit of microcurrent is called a magnetic dipole. The maximum torque generated by each unit of external magnetic field in vacuum on a magnetic dipole is the magnetic dipole moment Pm, and the vector sum of magnetic dipole moments per unit volume in the material is the magnetic polarization intensity J, with SI units in T (Tesla).

Nd-Fe-B permanent magnet is a tetragonal crystal system composed of Nd (neodymium), Fe (iron), and B (boron). It is the most practical and mass-produced permanent magnet material with the strongest magnetic properties, known as the "magnetic king". According to different preparation processes, Nd-Fe-B magnets can be divided into three categories: sintering, bonding, and hot pressing.

The magnetic performance indicators of permanent magnet materials mainly include residual magnetism (Br), magnetic induced coercivity (bHc), intrinsic coercivity (jHc), and maximum magnetic energy product (BH) max. In addition, there are several other magnetic performance indicators: Curie temperature Tc, working temperature Tw, residual magnetic temperature coefficient α、 Temperature coefficient of intrinsic coercivity β、 Recovery permeability μ Rec. Demagnetization curve squareness Hk/jHc....