COERCIVITY AND SPIN REORIENTATION TRANSITIONS IN ND-FE-B NANOCOMPOSITES PREPARED BY MELT-SPINNING

Alloys of composition Nd9Fe85B6, Nd11.76Fe82.46B5.88, and Nd18Fe76B6 w ere prepared by melt spinning at roll velocities from 19 to 25 m/s. Th e grain size distribution of rapidly quenched flakes was evaluated by means of X-ray diffraction line broadening, The average grain size of rapidly quenched Nd-Fe-B alloys is within a range from 19 to 40 nanome ters and differs from the roll contact side to the free side of the fl akes, For the first time, the spin reorientation transitions T-sr of n anophase Nd2Fe14B alloys have been determined, They were found to be l ower than that of bulk Nd2Fe14B. The smaller the grain size, the lower is T-sr. Also for the first time, the temperature dependence of the c oercivity of nanophase Nd-Fe-B magnets was determined from 4.2 to 300 K by measuring hysteresis loops on a single flake in a pulsed-field ma gnetometer with a field strength up to 24 MA/m. The coercivity of the nanophase Nd-Fe-B has less of a temperature dependence than sintered m agnets.