Point Defect Generation Probability in Rare-Earth Permanent Magnets in Radiation Environments via First-Principle Calculations

In recent years, rare-earth permanent magnets, including Nd ₂ Fe ₁₄ B and Sm ₂ Co ₁₇ , which are used in environments with high radiation, such as in electric motors for space equipment and robots operating in nuclear reactors, have become increasingly important. However, the demagnetization of the rare-earth permanent magnets induced by exposure to radiation has become a serious issue. In particular, when high-energy neutrons collide with the atoms in the magnet, the atoms can be removed and point defects can be generated. The spin fluctuations caused by point defects result in demagnetization of the rare-earth permanent magnets. In this study, we investigate via first-principle calculations, the probability of generation of point defects and the change in the magnetic moment in Nd ₂ Fe ₁₄ B and Sm ₂ Co ₁₇ that occurs as a result of the point defect creation. We find that the generation probability of the point defects is very similar in both rare-earth magnets. The attenuation of the magnetic moment in Sm ₂ Co ₁₇ was found to be considerably smaller than that of Nd ₂ Fe ₁₄ B. Thus, we conclude that the radiation resistance of the magnetic properties of Sm ₂ Co ₁₇ is higher than that of Nd ₂ Fe ₁₄ B.