Nitriding of Nd-Fe-B and Nd-Fe-C Hard Magnetic Alloys

Abstract

We have studied the effect of nitriding of Nd-Fe-B and Nd-Fe-C alloys by X-ray diffraction, Mössbauer spectroscopy, magnetization measurements and transmission electron microscopy. Samples were nitrided in an atmosphere of flowing NH₃ gas at temperatures between 300 and 500°C.
For the samples nitrided at 350, 375 and 400°C, interstitial dissolution of nitrogen atoms into Nd₂Fe₁₄B is assured by the extension of lattice constant of 0.2∼0.7%. Mössbauer spectroscopy shows that the increment of average hyperfine magnetic field of ⁵⁷Fe in the Nd₂Fe₁₄BN_x phase is 2∼4% as compared with that in the Nd₂Fe₁₄B phase. This is consistent with the result that the Curie temperature of Nd₂Fe₁₄BN_x is about 20 degrees higher than that of Nd₂Fe₁₄B. The samples nitrided above 400°C are almost amorphous.
Similar effects by nitriding, i.e. lattice expansion, increase in Curie temperature and that of hyperfine magnetic field, were also observed for Nd-Fe-C alloys.