Neutron diffraction analysis of melt spun 2:14:1 type (NdPr)–Fe–B compounds with Ti and Zr additions

Abstract

There has been continued technological and research interest in Nd2Fe14B-based compounds due to their excellent intrinsic magnetic properties [(BH)max*∼64 MGOe,Ha∼73 kOe]. It is found that Ti and Zr substitution in Nd2Fe14B leaves its magnetic properties largely unaffected. We have carried out neutron diffraction studies on Zr and Ti substituted 2:14:1 compounds. Three specimens of melt spun alloys of compositions (Nd0.75Pr0.25)12Fe80B8, (Nd0.75Pr0.25)8.4Fe79.7Ti4.7B7.2 and (Nd0.75Pr0.25)9.2Fe79.2Ti2Zr2.2B7.4 were studied. Rietveld refinements reveal that the 4f site is equally occupied by Nd and Pr while the 4g site is occupied only by Nd. In the Ti-containing sample, the lattice expands and Ti is found on the j1, j2 sites normally occupied by Fe, (4% and 8%, respectively). This accounts for about 30% of the added Ti. In the third sample, the lattice contracts, which could occur only if Zr replaces the larger rare-earth atoms. However, due to the possibility of four different species occupying the 4f site (i.e., Nd, Pr, Ti, and Zr), it is not possible to determine their relative concentrations from neutron diffraction data alone. The balance of Ti and Zr in this sample must be locked in the grain boundaries. Despite peak broadening associated with the fine grain structure, robust refinements were achieved.