Magnetic hardening of Pr-Fe and Nd-Fe alloys by melt-spinning

Abstract

The dependence of the hard magnetic properties of melt-spun Nd1−xFex (0.5⩽x⩽0.7) and Pr1−xFex (0.4⩽x⩽0.7) alloys on quench rate is reported; the latter was controlled by varying the substrate surface velocity (vs ) of the melt-spinner. All of the alloys show an appreciable maximum in coercivity (Hci ) as a function of quench rate. For Nd1−xFex , a peak room temperature Hci of 8.65 kOe was found for a Nd0.5Fe0.5 alloy. Room-temperature coercivities of ∼7.5 kOe were found in Pr1−xFex over the interval 0.6⩽x⩽0.7. The temperature dependence of the coercivity changed from a 1/T dependence for the most amorphous alloys to exponential for the alloys exhibiting maximum coercivity; coercivities as high as 78 kOe were found at 20 K. X-ray data indicate that the coercive force results from an amorphous and/or very finely crystalline microstructure whose average particle size and/or intrinsic anisotropy varies as a function of quench rate. Crystallization studies, using differential scanning calorimetry and x-ray diffraction, found the Nd1−xFex and Pr1−xFex alloys to form a number of nonequilibrium phases but could not establish whether these phases formed from an amorphous or metastable crystalline precursor. Depending on quench rate, the melt-spun Nd1−xFex alloys appear to form distinctly different nonequilibrium phases, indicating that the magnetically hard precursor may also vary with quench rate.