The influence of a negative surface anisotropy on a coercivity H_c has been investigated within a framework of the micromagnetics calculations. The model of a permanent magnet obtains the negative index of a surface anisotropy, which affects the reduction of H_c. The influence of the surface anisotropy also reduces the dependence of the misdirection of an applied field. Accordingly, it is thought that the reduction of the H_c due to the misorientation of the crystal grains is inhibited in the polycrystalline magnet.
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