Abstract
We have investigated the effect of HoH2 hydride addition on the hysteresis loop parameters of sintered Pr-Fe-Ti-Al-Cu-B magnets. The magnets were prepared by traditional powder metallurgy technology, and 3 wt.% HoH2 was added to the powder at the fine-milling stage. The magnets exhibited a monotonic increase in all hysteretic parameters with decreasing temperature down to 4.2 K. The coercive force and maximum energy product at 295 K (4.2 K) were 1344 (5402) kA/m and 221 (336) kJ/m3, respectively. The structure of the magnets was studied in detail by scanning electron microscopy and energy dispersive X-ray spectroscopy, which demonstrated the formation of the so-called “core-shell” structure, which is assumed to favor the marked improvement in the hysteretic properties of the samples analyzed. The surface domain structure was measured in the directions perpendicular and parallel to the magnet texture using magnetic force microscopy. The data obtained indicated fine labyrinth-like and strip domain patterns in the directions perpendicular and parallel to the magnet texture, with an average domain width of 1.2–1.8 µm.
Highlights
In recent years, permanent magnets based on (Pr, Nd)2Fe14B compounds have become potential candidates for applications at low temperatures.1–3 Nd2Fe14B-based magnets with a high remanence cannot be employed for the construction of undulators because of their weak coercivity at room temperature (RT)
The structure of the magnets was studied in detail by scanning electron microscopy and energy dispersive X-ray spectroscopy, which demonstrated the formation of the so-called “core-shell” structure, which is assumed to favor the marked improvement in the hysteretic properties of the samples analyzed
The tilting angle increases with decreasing temperature and, as a result, the remanence drops below values corresponding to RT
Summary
Permanent magnets based on (Pr, Nd)2Fe14B compounds have become potential candidates for applications at low temperatures (undulators, magnetic bearings, wigglers, etc.). Nd2Fe14B-based magnets with a high remanence cannot be employed for the construction of undulators because of their weak coercivity at room temperature (RT). The Pr2Fe14B-based magnets exhibit no SRT down to 4.2 K.7,8 All these factors make Pr-Fe-B alloys attractive for wide temperature range applications. This fact determines the higher quenching rates and assumes the application of hydrogen decrepitation It was shown in Reference 10 that the presence of hydrogen changes the anisotropic nature of Prl5Fe79B6 hydrogenated powders from uniaxial to planar in the range 4250–4500 ppm H2. If the hydrogenated Pr2Fe14B powder is compacted in a magnetic field, no texturing along the easy-magnetization axis takes place, and the powder behaves to an isotropic system at RT. In this case, the hysteretic parameters of the magnets decrease abruptly. The aim of the present study was to investigate the effect of HoH2 additions, which were subjected to fine milling together with the hydrogenated PrFeBHx alloy, on the texture formation and properties of permanent magnets over the wide temperature range 4.2–295 K
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