Abstract
The FexNd100-x (x = 14, 28) alloys were successfully prepared by melt-spinning. Hysteretic and thermomagnetic properties of the as-melt-spun alloys and short-aged ribbons were investigated. Both ribbons exhibit a soft magnetic behavior at room temperature but at 5 K, the coercive force (Hci) proliferated to 8.6 kOe and 11.7 kOe, respectively. Thermomagnetic measurements, Zero Field Cooling (ZFC) and Field Cooling (FC), demonstrated that the rise in magnetization of the ribbons at temperatures lower 34 K is associated with ferromagnetism of fcc Nd-Fe solid solution clusters. Positive effect of aging on the coercivity of the Fe14Nd86 and Fe28Nd72 ribbons was observed. At 300 K, Hci of the ribbons upsurge to 2 - 2.8 kOe after aging at 400 - 450°C for 15 minutes but sharply diminished after aging at temperatures higher than 500°C. It was suggested that the increase in RT coercivity during aging was as a result of the decomposition of the amorphous phase and formation of the hard magnetic Fe-rich clusters. For both ribbons aged at 500°C, the magnetic transition at 340 K was observed to be in relation to the TC of the Nd2Fe17 compound. The appearance of this soft magnetic phase in the microstructure of the aged ribbons was linked with the drastic diminution of the coercivity at that temperature.
Highlights
The interest in the study of the Nd-Fe alloys was renewed during the last decades owing to the significant role Nd-rich intergranular phase play in the development of high coercivity of sintered Nd-Fe-B-based magnets
Comparing the Zero Field Cooling (ZFC) and Field Cooling (FC) curves for Nd and Fe14Nd86 ribbon at temperatures lower than 50 K shows the magnetic transitions at ≈ 9 K, ≈ 17 K and ≈ 34 K in both Nd and ribbon
According to [9], the first two transitions correspond to antiferromagnetic ordering temperature of the dhcp Nd. This suggests that the ferromagnetic transition at 34 K is related to the metastable fcc allotrope of Nd or Nd-Fe solid solution (Nd-based nanocrystals) [6,7]
Summary
The interest in the study of the Nd-Fe alloys was renewed during the last decades owing to the significant role Nd-rich intergranular phase play in the development of high coercivity of sintered Nd-Fe-B-based magnets. The first is the effect of the thin layers between the Nd2Fe14B grains which consists of amorphous Nd-Fe phase These layers act to reduce or remove defects at the Nd2Fe14B grain surfaces. The microstructure of as-melt-spun Nd-rich alloys consists of an amorphous-like region composed of nanocrystals of unknown phase embedded in an amorphous matrix [6,7]. It is, expected that aging may lead to additional decomposition of the amorphous phase and formation of the microstructure similar to the one responsible for the high coercivity in as-cast Nd-rich alloys.
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