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

Alloys of composition Nd₉Fe₈₅B₆, Nd_11.76Fe_82.46B_5.88, and Nd₁₈Fe₇₆B₆ 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_ST of nanophase Nd ₂Fe₁₄B alloys have been determined. They were found to be lower than that of bulk Nd₂Fe₁₄B. The smaller the grain size, the lower is T_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