Abstract: The present application relates to a technical field of determining an irreversible demagnetization of a grain boundary diffusion NdFeB magnet, and more particularly, to a method for identifying an irreversible demagnetization of a grain boundary diffusion NdFeB magnet by magnetic field distribution. After applying a reverse magnetic field to a saturatedly magnetized grain boundary diffusion NdFeB magnet, if a number of magnetic poles on a non-diffusion face of the grain boundary diffusion NdFeB magnet is increased, it is determined that there is an irreversible demagnetization in the grain boundary diffusion NdFeB magnet.

Abstract: The present application relates to a preparation method of neodymium iron boron products and the neodymium iron boron product prepared by using the same. The preparation method of neodymium iron boron products includes the following steps: Step S1: preparing blank magnet; Step S2: obtaining preprocessed sheets; Step S3: surface treating; Step S4: heavy rare earth coating; Step S5: stacking: stacking a plurality of preprocessed sheets to give stacked magnets; and Step S6: grain boundary diffusion: successively subjecting the stacked magnets to a primary heat treatment for 2-40 min, a secondary heat treatment at 700-1000° C. for 4-40 h, and then tempering at 450-700° C., in which the primary heat treatment is induction heat treatment or electric spark sintering.