Micromagnetics Simulation of High Energy Density Permanent Magnets
Dieter Süss, Thomas Schrefl, and Josef Fidler
IEEE Trans Magn., 35 (1999) 3223-3228.
A finite element approach is used to calculate the influence of different
grain boundary phases on the reversal process of sintered Nd-Fe-B magnets.
To calculate equilibrium states of the magnetic polarization the total Gibbs
free energy is minimized with a quasi-Newton conjugate gradient method.
It was found that the grain boundary phases influence the coercive field
significantly. For a perfect microstructure the numerical results agree well
with the Stoner Wohlfarth theory. A reduction of the magnetocrystalline
anisotropy near grain boundaries leads to a linear decrease of the coercive
field. In contrast to the Stoner Wohlfarth theory the coercive field will
decrease with increasing alignment of the easy axies if the anisotropy is
reduced near grain boundaries. The finite element simulations confirm the
experimental results that nonmagnetic Nd-rich phases at grain boundary
junctions significantly increase the coercive field.
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Feb. 13, 2001