WHAT DETERMINES THE DEMAGNETIZATION IN ND-FE-B MAGNETS

In order to understand the demagnetization in Nd-Fe-B magnets the demagnetization curve J(H) is calculated, which demonstrates that realistic J(H) curves can be simulated. The coercivity is therefore determined by the difference between the nucleation fields of the individual grains and the locally effective counterfields originated by grains that are already reversed. If adjacent grains are exchange coupled, the coercivity will be decrease linearily with an increasing number of exchange couplings. Realistic J(H) curves can be simulated for nucleation fields of 75% of the anisotropy field, internal counterfields of 32 kOe and 40% exchange-coupled grains.