The structure and magnetic properties of rapidly quenched and annealed multi-phase nanocrystalline Nd9Fe91-xBx ribbons

Melt-spun and annealed Nd9Fe91-xBx ribbons with 0 less than or equal to x less than or equal to 9 have been studied by means of X-ray diffraction, thermomagnetic analysis and magnetic measurements. The metastable phase diagram up to 780 degrees C has been plotted. A metastable phase of the TbCu7 structure has been identified in the ribbons of binary composition and those containing up to 7 at.% B. The Curie temperature of this phase was found to be strongly affected by both boron content and annealing temperature. The structure of exchange coupled nanocrystallites of Nd2Fe14B, alpha-Fe and Fe3B was realized by means of short-time annealing. The annealed isotropic Nd9Fe84B7 ribbons had a remanence of 100.5 emu g(-1), an intrinsic coercivity of 4.5 kOe, and an energy product of about 13 MG Oe. The details of structure formation, as well as the criteria and conditions for the effective exchange coupling, are discussed.