Hard magnetic bulk amorphous alloys

Abstract

An amorphous phase in Ln-Fe-Al (Ln=Nd and Pr) systems is formed in wide composition ranges of 0 to 90 at% Fe and 0 to 93 at% Al by melt spinning. Ferromagnetic Ln/sub 90-x/Fe/sub x/Al/sub 10/ bulk amorphous alloys with high coercive force (/sub i/H/sub c/) at room temperature are obtained by copper mold casting. The maximum diameter of the cylindrical amorphous samples is 12 mm for the Nd-30%Fe-Al alloy and 3 mm for the Pr-30%Fe-Al alloys and decreases with deviating Fe content. The extremely high T/sub x//T/sub m/ and small /spl Delta/T/sub m/(=T/sub m/-T/sub x/), which are evaluated by the crystallization temperature (T/sub x/) and melting temperature (T/sub m/), are the reason for the achievement of large glass-forming ability in these systems. The bulk amorphous Ln/sub 60/Fe/sub 30/Al/sub 10/ alloys are ferromagnetic with the Curie temperature of 515 to 600 K which are higher than those for Nd-Fe and Pr-Fe binary amorphous ribbons. The remanence and /sub i/H/sub c/ are 0.089 to 0.122 T and 277 to 321 kA/m, respectively and the crystallization to Ln+Al/sub 2/Ln+/spl delta/ causes a ferromagnetic-to-paramagnetic transition. Thus, the hard magnetic properties are achieved only in the amorphous state.