Journal of the Magnetics Society of Japan

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The phase boundary between tetragonal Nd₂Fe₁₄B phase and fcc Nd-rich phase in Nd-Fe-B sintered magnets was investigated with a high-resolution transmission electron microscope. Two types of crystallographic orientation relationships were detected between two phases in direct contact; (110)_tetra. // (110)_fcc, [001]_tetra. // [223]_fcc and (110)_tetra. // (010)_fcc, [001]_tetra. // [102]_fcc. The atomic structure of the phase boundary, based on the coincidence site lattice model, was modeled, and agreed with the observed relationships. The effective anisotropic coefficient K_eff at the Nd sites near the boundary was calculated to be 2.72 × 10⁶ J/m³ by using the point charge model when no account was taken of the Nd-rich phase. K_eff increases to 4.37 × 10⁶ J/m³ when the point charge of Nd³⁺ in the Nd-rich phase is taken into account, since the positive charge of the cation enhances the magnetocrystalline anisotropy near the boundary, where the nucleation of the reverse domain may be suppressed.

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