from the conferences organized by TANGER Ltd. provisional website
Sintered permanent magnets based on the Nd2Fe14B intermetallic compound are widely used in industry as a rule in a temperature range of from -60 to 150 °C. However, in recent years, there appears a need to use such magnets at cryogenic temperatures and mainly at liquid nitrogen temperature (77 K). The natural increase in Br of Nd-Fe-B magnets with falling temperatures is well known phenomenon but it is limited to temperatures above 135 K due to the spin-reorientation in Nd2Fe14B-based alloys. At this temperature, the easy-axis magnetic anisotropy changes to easy-axes cone anisotropy. The Pr2Fe14B compound exhibits no spin-reorientation transition up to cryogenic temperatures. Therefore, permanent magnets based on Pr2Fe14B compound are of interest for investigators owing to the capability of these magnets to remain high hysteretic parameters at low and cryogenic temperatures. In this case, the natural increase in the hysteretic parameters with decreasing temperature can be adequately used. The Pr2Fe14B-based magnets (Pr-Fe-Ti-Al-Cu-B) were prepared by traditional powder metallurgy technology, and 3 wt.% HoH2 was added to the main powder at the fine-milling stage. The structure of the magnets was studied in detail by scanning electron microscopy (SEM/EDX) and the formation of pronounced so-called “core-shell” structure was demonstrated. The effect of HoH2 hydride addition on the hysteresis loop parameters of sintered Pr-Fe-Ti-Al-Cu-B magnets was studied and the marked improvement of hysteretic parameters was found. Domain structure of the magnets was studied perpendicular and parallel to the magnet texture using magnetic force microscopy. The data obtained indicate the well-formed magnetic texture. The average domain width is 1.2-1.8 m.Keywords: Pr-Fe-B magnets, coercive force, core-shell structure, SEM, low-temperature hysteretic properties
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