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

The effects of Zr and Co substitutions for Fe on the magnetic properties of nanocrystalline near-stoichiometric (Nd_0.75Pr _0.25)₁₂(Fe_1-xCo_x)_82-z Zr_zB₆ (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)_max (~160 kJ/m³) and intrinsic coercivities, _iH_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_c. For alloys in which, also, 10 and 20% of the Fe was substituted by Co, excellent remanence enhancement, J_r (to >1 T) were achieved with 1 at% Zr addition. Combined with excellent squareness of the J-H second quadrant, this gave (BH)_max up to 175 kJ/m³, together with Curie temperatures, T_c of >375°C and >460°C for 10 and 20% Co, respectively, and with only minor reductions in _iH_c. The role of Zr in promoting uniform and refined grain structures and enhancing the magnetic properties will be discussed