Structure and magnetic characterization of amorphous and crystalline Nd-Fe-Al alloys

Glass formation has been studied in Nd60Fe30Al10 alloy produced by melt-spi nning, water quenching and copper mold chill casting. Partially amorphous a lloys were obtained by melt-spinning at low wheel speeds of 5 to 15 m/s and by water quenching of a 1-mm diameter rod, while fully amorphous alloys we re obtained by melt-spinning at higher wheel speeds of 20 and 30 m/s and ch ill casting of a 1-mm diameter rod. A high coercivity was observed in the p artially amorphous ribbon melt-spun at 5 m/s and water quenched rod, and in the fully amorphous chill cast rod, while low values of coercivity were ob tained in fully amorphous ribbons melt-spun at high speeds of 20 and 30 m/s . Crystallization of water quenched and chill cast samples after heat treat ment at high temperature resulted in a substantial reduction of the high co ercivity. Results of X-ray diffraction indicate that formation of Nd and a ternary Fe-Nd-Al phase with an unknown crystal structure were present after crystallization. TEM results and a magnetic study of the heat treated samp les indicate that as long as there is an amorphous phase produced by low co oling rate, the high coercivity remains. The high coercivity of bulk amorph ous samples is discussed. The unknown ternary Fe-Nd-Al phase is antiferroma gnetic with a Neel temperature at about 260 K. (C) 1999 Elsevier Science S. A. All rights reserved.