Micromagnetics of nanocrystalline permanent magnets

Micromagnetic finite element calculations provide the theoretical limits for the remanence, the coercive held, and the coercive squareness of nanocomposite Nd2Fe14B/alpha-Fe,Fe3B,Fe23B6 magnets. The influence of the intrinsic magnetic properties and the microstructure were investigated using an energy minimization technique. The coercive field reaches a maximum as a function of the average grain size at about 15 nm - 20 nm. The replacement of alpha-Fe with Fe3B improves the coercive field but deteriorates the loop shape. The reduction of the magnetization and the exchange constant in the soft magnetic Fe3B phase by 20% improves the coercive held without a significant loss in the remanence. An increase of the hard phase anisotropy by 8% enhances the coercive field by more the 100 kA/m in two-phase alpha-Fe/Nd2Fe14B and by 60 kA/m in two-phase Fe3B/Nd2Fe14B magnets. Dynamic simulations for magnetostatically interacting particles of a bonded magnet show a slight influence of the particle arrangement on magnetization reversal. The interaction field in the range of 100 kA/m to 200 kA/m rapidly decreases the distance from the particle.