Crystallization and hard magnetic properties of Fe-Co-Nd-Dy-B amorphous alloys with glass transition

Glass transition followed by a supercooled liquid region was observed in the composition range of 4-56 at. %Co, 2-4.5 %Nd, 0-1.25 %Dy, and 18-30 %B in melt-spun Fe-Co-Nd-Dy-B amorphous alloys. The largest value in the supercooled liquid region (Delta T-x) was 45 K for Fe66.5Co9.5Nd3.5Dy0.5B20. The crystallized structure consists of 2:14:1, Fe3B, and alpha-(Fe, Co) phases and their grain sizes after annealing for 420 s at 933 K are 15, 15, and 50 nm, respectively. The interparticle spacing of the 2:14:1 phase is less than 50 nm. The remanence (B-r), coercivity (iH(c)), and maximum energy product (BH)(max) after an optimum annealing treatment (933 K, 420 s) are 1.24 T, 263 kA/m, and 92 kJ/m(3), respectively, for the Fe66.5Co9.5Nd3.5Dy0.5B20 alloy. The rather good hard magnetic properties are interpreted to result from the exchange magnetic coupling among 2:14:1, Fe3B, and alpha-(Fe, Co) phases. The good hard magnetic properties in the crystallized state of the Fe-Co-Nd-Dy-B amorphous alloys with large Delta T-x over 40 K are expected to enable the future fabrication of a bulk hard magnetic material by the simple process of the formation of a bulk amorphous alloy followed by optimum crystallization. (C) 2000 American Institute of Physics. [S0021-8979(00)51608-9].