Improvements in the Coercivity of Iron-Based Nanocrystalline Low-Rare-Earth Fe3B-Nd Permanent Magnets

Abstract

Fe <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> B-based Nd-Fe-B permanent magnet materials containing Co and M as additives (M=Al, Si, Cu, Ga, Ag, Au) were prepared in an extremely low rare-earth concentration range centered on 4 at%. The hard magnetic properties develop as a result of heat treatment of rapidly solidified amorphous ribbons, which produces a metastable nanocrystalline structure consisting of Fe <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> B and Nd <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> Fe <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">14</sub> B. Use of the additives considerably reduces the crystallite sizes, and consequently the alloys exhibit higher coercivity than that seen in alloys without additives. Compaction-molded resin-bonded magnets produced from such Nd-Fe-B-Co-M materials have the following magnetic properties: H <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">cj</sub> =300 kA/m to 470 kA/m; B <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">r</sub> =0.7 T to 0.9 T; (BH) <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">max</sub> =50 kJ/m <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup> to 73 kJ/m <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup> . Typical values for the temperature coefficients of B <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">r</sub> and H <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">cj</sub> of bonded magnets are -0.05%/K and -0.35 %/K, respectively, in the range from 297K to 413K.