EFFECT OF AGING ON THE MAGNETIC PROPERTIES OF RAPIDLY QUENCHED Nd-rich Nd-Fe ALLOYS
The interest in the study of the Fe-Nd alloys was renewed during last decade owing to the important role Nd-rich intergranular phase in the formation of high coercivity of sintered Nd-Fe-B-based magnets. High coercivity values in as-cast Nd-rich Fe-Nd alloys were correlated to a metastable eutectic microstructure which includes hard magnetic phase (Ax) with unidentified structure and composition . The formation mechanism of Ax magnetic phase during cooling of the Fe-Nd alloys and its structure-property relationship remain unknown yet. Therefore, the aim of this work was to study the effect of aging temperature on the magnetic properties of the melt-spun Nd-rich Nd-Fe alloys.
The FexNd100-x alloys (x = 14, 28) were prepared by melting pure metals of Nd and Fe in an argon arc furnace. The ingots were quenched by melt-spinning with a copper-wheel at a velocity approximately 40 m×s-1 to prepare ribbons. Magnetic measurements at temperatures 5 K and 300 K were measured using a PPMS EverCool-II magnetometer in a maximum magnetising field of 9T and 5T respectively. The aging of the ribbons was performed in a vacuum furnace at temperatures ranging 300–650oC for 30 min. The hysteresis loops in the magnetisation field of 5T and 9T were studied. The temperature dependence of magnetization on zero-ﬁeld cooled and ﬁeld cooled for the aged ribbons were also measured.
The un-aged sample tested under 300 K-5 T gave Hci of least values of 74 and 4 Oe for the ribbons x = 14 and 28, respectively (Fig. 1a). Maximum values of 3.1 kOe and 2.6 kOe were received after aging at 450oC for 30 minutes for ribbons x = 14 and 28, respectively. But aging at temperatures from 500oC and above decreased the Hci, lower than 200 Oe, for both ribbons. At 5 K-9 T, coercive forces as high as 8.6 and 11,7 kOe were observed for the initial ribbons with x = 14 and 28 respectively (Fig. 1b). Increasing the aging temperature from 300 to 575oC resulted in the coercive forces of the ribbon x = 14 decreasing monotonically from 6,6 to 0,1 kOe. There was also a drastic decrease in the coercive force, from 10.8 KOe to 1.2 KOe, for the ribbon x = 28 between 450 and 500oC. Zero-field and field cooling characteristics of aged Fe-Nd ribbons were discussed.
 V.P. Menushenkov, I.V. Shchetinin, M.V. Gorshenkov, A.G. Savchenko, S.V. Ketov, IEEE Magn. Lett., 7 (2016) 5201304.