Crystallization behavior and magnetic properties of melt-spun Pr/sub x/(Fe/sub 0.8/Co/sub 0.2/)/sub 94-x/B/sub 6/ alloys

Abstract

The influence of Pr content on the crystallization behavior of amorphous Pr (Fe 0 8 Co 0 2 ) 94 B 6 ( = 12 10 9 8) melt-spun ribbons and the magnetic properties following annealing have been systematically investigated. The results show that, depending on the Pr content, the phase evolution of the ribbons during crystallization occurs via different sequences. The optimal annealing conditions required rapid heating through or beyond the temperatures for the final transformation stage. For = 12 ribbons, very good second-quadrant loop shape and magnetic property combinations ( = 755 kA/m, ( ) max = 160 kJ/m 3 ), though somewhat lower than those obtained by directly quenching to the nanocrystalline state, were obtained after optimal annealing. However, for the substoichiometric alloys ( = 10 9 8), the loop shapes and magnetic properties for optimally annealed ribbons ( = 270 400 kA/m, ( ) max = 70 120 kJ/m 3 ) were inferior to their directly quenched counterparts because of lower nucleation frequencies and, thus, coarser grain structures. Index Terms-Magnetic properties, metastable phase, nanocomposite magnets, phase transformation.

Explosive shock processing of Pr2Fe14B/α–Fe exchange-coupled nanocomposite bulk magnets

“…Nanocomposites with such characteristics have been recently shown to have significantly improved magnetic properties. [4][5][6][7][8] However, these nanocomposites have been typically produced in the form of powders or thin films, and there exist major obstacles in producing bulk nanocomposite magnets. Conventional sintering and hot-pressing methods, which are usually used to produce single-phase microcrystalline permanent magnets, are not favored in making bulk nanocomposite magnets because it is difficult to avoid grain growth during these processes.…”

The role of sub-micron grain size in the development of rare earth hard magnetic alloys

“…In the case of the OQA alloys, nucleation and growth of crystals takes place at much lower temperatures, in a regime of much lower nucleation frequencies than for the DQ alloys. Hence, fewer, but larger, ␣-Fe crystals would be expected in the former than in the latter [24]. TEM studies on these alloys [17,21] provide evidence to support this proposition the OQA alloys having a unimodal distribution of grain sizes centred at ∼40 nm, in contrast to the DQ alloys which showed a clearly bimodal distribution with one peak centred at ∼15 nm, corresponding to ␣-Fe, and another centred typically at ∼40-45 nm, corresponding to the RE 2 Fe 14 B grains.…”