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).
On the demagnetization curve of a permanent magnet, when the reverse magnetic field H increases to a certain value bHc, the magnetic induction intensity B of the magnet is 0, and the reverse magnetic field H value is called the magnetic induction coercivity bHc of the material; When the reverse magnetic field H=bHc, the magnet does not display magnetic flux externally, and the coercive force bHc characterizes the ability of the permanent magnet material to resist external reverse magnetic fields or other demagnetization effects. The coercive force bHc is one of the important parameters in magnetic circuit design.
When the reverse magnetic field H=bHc, although the magnet does not show magnetic flux to the outside, the magnetic polarization intensity J of the magnet still maintains a large value in the original direction. Therefore, bHc is not sufficient to characterize the intrinsic magnetic properties of the magnet. When the reverse magnetic field H increases to jHc, the vector sum of the microscopic magnetic dipole moments inside the magnet is 0, and this reverse magnetic field H value is called the intrinsic coercive force jHc of the magnet. The intrinsic coercivity jHc is a very important physical parameter of permanent magnet materials, which is a main indicator of the ability of permanent magnet materials to resist external reverse magnetic fields or other demagnetization effects to maintain their original magnetization state.