Composition and Microstructure Dependent Spin Reorientation in Nanocrystalline (Nd–Pr)-(Fe–Co)-B Alloys

Abstract

The effects of composition, grain size and exchange coupling on the spin-reorientation temperature (T/sub SR/) for nanocrystalline (Nd-Pr)-(Fe-Co)-B alloys have been systematically studied. Although T/sub SR/ is usually considered to be an intrinsic magnetic property, it is nevertheless influenced by the microstructure when the grain size decreases to the nanometer level. The T/sub SR/ for all single phase nanocrystalline Nd/sub 12/Fe/sub 82/B/sub 6/ alloys were lower than the published value for a single crystal or for an aligned sintered NdFeB magnet. The results consistently demonstrate that the increasing degree of exchange coupling between the RE/sub 2/Fe/sub 14/B nano-grains with decreasing grain size leads to a progressive decrease in T/sub SR/. As is the case for conventional NdFeB alloys, Pr substitution for Nd decreases T/sub SR/ linearly and rapidly with increasing Pr concentration but a spin reorientation still occurs at 75% Pr substitution (T/sub SR//spl ap/25 K). Co substitution for Fe also decreases T/sub SR/, but to a lower degree than Pr for Nd. Introduction of an increasing volume fraction of soft magnetic /spl alpha/-(Fe-Co) phase into the nanocrystalline Nd/sub 2/Fe/sub 14/B alloy has no significant influence on the value of T/sub SR/ in spite of the influence of /spl alpha/-(Fe-Co) on the exchange coupling.