Micromagnetic theory of the pinning of domain walls at phase boundaries

Planar phase boundaries in hard-magnetic materials are found to act as strong repulsive or trapping barriers for the displacement of domain walls if the magnetocrystalline anisotropies of the two phases are different from each other. On the basis of the continuum theory of micromagnetism the coercive field of the phase boundaries is determined under the general conditions of different material parameters of the two phases (spontaneous magnetization J_s, magnetocrystalline anisotropy K₁, exchange constant A). The results are applied to analyze the coercive field of the three-phase nanocrystalline Sm ₂Co ₁₇-based magnets.