High coercivity Zr and Co substituted (Nd-Pr)-Fe-B nanophase hard magnetic alloys

Abstract

The effects of Zr and Co substitutions for Fe on the magnetic properties of nanocrystalline near-stoichiometric (Nd/sub 0.75/Pr/sub 0.25/)/sub 12/(Fe/sub 1-x/Co/sub x/)/sub 82-z/Zr/sub z/B/sub 6/ (x=0,0.1,0.2 and z=0-4) alloy ribbons are reported. The nanoscale structures were derived by devitrification annealing of amorphous as-cast ribbon. Very good combinations of energy product, (BH)/sub max/ (/spl sim/160 kJ/m/sup 3/) and intrinsic coercivities, /sub i/H/sub c/ (within the range 800-1400 kA/m for various Zr concentrations) were achieved for the Co-free alloys although the Zr addition resulted in some reduction in T/sub c/. For alloys in which, also, 10 and 20% of the Fe was substituted by Co, excellent remanence enhancement, J/sub r/ (to >1 T) were achieved with 1 at% Zr addition. Combined with excellent squareness of the J-H second quadrant, this gave (BH)/sub max/ up to 175 kJ/m/sup 3/, together with Curie temperatures, T/sub c/ of >375/spl deg/C and >460/spl deg/C for 10 and 20% Co, respectively, and with only minor reductions in /sub i/H/sub c/. The role of Zr in promoting uniform and refined grain structures and enhancing the magnetic properties will be discussed.