Investigation of intergrain exchange coupling interaction of nanocrystalline permanent magnets by numerical simulation

The initial curves, demagnetization curves and recoil curves of Pr2Fe14B and Pr2Fe14B-α Fe nanocrystalline permanent magnets have been calculated by micromagnetic finite_element method. The validity of δm(H)curves, which can be used to determine the strength of intergrain exchange coupling interaction (IGEC), is approved by the calculated results. It is found that IGEC weakens with increasing grain size D for single-phase nanocrystalline and nanocomposite permanent magnets. Thus, the demagnetization curve shows a two-phase behavior and the δm(H) curve shows two peaks for the nanocomposite sample with D=20nm.The peak at small field can be attributed to the exchange interaction between the magnetic hard and soft grains, while the peak at large field may be due to the IGEC among hard grains.