MAGNETIC-PROPERTIES OF CR-ADDED ND-FE-B N ANOCRYSTALLINE COMPOSITE MAGNETS

By means of Fe-57 Mossbauer spectroscopy, X-ray diffraction and magnet ization measurements, the magnetic properties and phase compositions o f Cr-added Nd-Fe-B nanocrystalline composite magnets, Nd-4.5(Fe1-xCrx) (77) B-18.5 (x = 0, 0.013, 0.039, 0.065, 0.130, 0.260), have been inve stigated as a function of the Cr concentration. With increasing Cr con tent, the coercivity of the specimen increases, but the remanence decr eases. In all the specimens, hard magnetic Nd2Fe14B crystallizes and i ts amount increases with increasing Cr concentration. Such an increase in the amount of the hard magnetic compound results in an increase of coercivity. The amount and kind of the soft magnetic phase formed var ies with the Cr content. The specimen with low Cr content consists of both Nd2Fe14B and Fe3B. On the other hand, the specimen which contains a large amount of Cr consists of Nd2Fe14B-(Fe2B, alpha-Fe) nanocrysta lline composite. From the Mossbauer measurements, it is found that the hyperfine magnetic fields of both Nd2Fe14B and alpha-Fe in the specim ens are almost independent of the Cr content. The hyperfine magnetic f ield of the Fe-B compound decreases as a function of the Cr content, a nd consequently Fe2B in Nd-4.5(Fe-0.74 Cr-0.26)(77)B-18.5 contains a l arge amount of Cr and becomes non-magnetic at: room temperature. These results suggest that the Cr atoms mainly exist in the Fe-B compound, not in the Nd2Fe14B and alpha-Fe compounds, and reduce the magnetizati on and the Curie temperature of the Fe-B compound. Moreover, the total amount of the soft magnetic phases decreases with increasing Cr conte nt. These are the origins of the decrease in remanence of Nd-Fe-B-Cr n anocrystalline composite magnets.