Improvement in coercivity by high-speed crystallization for PrFeB magnets

Abstract

Summary form only given. A formation of a fine nano-structure is a key point to obtain spring ones. Therefore, we tried to form nano-crystallized texture by increasing a heating rate for annealing. After preparing amorphous Pr/sub 10.5/Fe/sub 84.5/B/sub 5/ flakes by the rapid-quenching method, the samples were annealed under the heating rate of 60, 300 and 850 K/min. For a further increase in the heating rate, the pulse annealing was carried out by controlling the output power of an infrared furnace, and samples were crystallized during 1.5-4 s. The increase in the heating rate refined the Pr/sub 2/Fe/sub 14/B grain size and achieved enhanced coercivity and slight improvement in remanence. Consequently, (BH)max was improved significantly, and we could obtain superior magnetic properties at the heating rate of 850 kA/m; Mr=1.3 T, Hc=450 kA/m, and (BH)max=150 kJ/m3. These results suggest that an increase in heating rate is a promising way of improving magnetic properties of PrFeB exchanged-spring magnets. It was also found that a further increase in heating rate is an effective way to improve the squareness of a demagnetization curve. These improvements suggest that high-speed crystallization leads to decrease the grain size and form a fine nano-crystallized texture.