NUCLEATION OF REVERSED DOMAINS AT GRAIN-BOUNDARIES

Micromagnetic analysis using a finite-element technique confirms that intergrain magnetostatic and exchange interactions drastically affect the magnetization reversal mechanism in nucleation controlled permanent magnets. The investigation of the nucleation fields of magnetically coupled grains emphasizes the important role of nonmagnetic boundary phases and well-aligned grains for the enhancement of coercivity. The long-range magnetostatic interactions between the grains reduce the coercive field of ideally oriented particles. The exchange coupling of misoriented neighboring grains causes a strongly inhomogeneous magnetic state near the interface of the particles which favors the nucleation of reversed domains. Intergrain exchange interactions considerably reduce the coercive field, especially if the angle between the easy axes of adjacent grains is high. An algorithm for adaptive mesh refinement controls the discretization error throughout the calculation of the demagnetization curves.