Coercivity and spin reorientation transitions in Nd-Fe-B nanocomposites prepared by melt spinning

Abstract

Alloys of composition Nd/sub 9/Fe/sub 85/B/sub 6/, Nd/sub 11.76/Fe/sub 82.46/B/sub 5.88/, and Nd/sub 18/Fe/sub 76/B/sub 6/ were prepared by melt spinning at roll velocities from 19 to 25 m/s. The 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 nanometers and differs from the roll contact side to the free side of the flakes. For the first time, the spin reorientation transitions T/sub ST/ of nanophase Nd/sub 2/Fe/sub 14/B alloys have been determined. They were found to be lower than that of bulk Nd/sub 2/Fe/sub 14/B. The smaller the grain size, the lower is T/sub ST/. Also for the first time, the temperature dependence of the coercivity 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 magnetometer 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 magnets.