Preparation of bulk Pr-Fe-Al amorphous alloys and characterization of their hard magnetic properties

The amorphous phase in the Pr-Fe-Al system is formed in an extremely wide composition range of 0 to 90 at% Fe and 0 to 93 at% Al by melt spinning. Ferromagnetic Pr90-xFexAl10 bulk amorphous alloys with high coercive force at room temperature are obtained by a copper mold casting method. The maximum diameter of the cylindrical amorphous samples with a length of 50 mm is 3 mm for the 30%Fe alloy and 1 mm for the 20%Fe, 40%Fe and 50%Fe alloys. Neither the glass transition nor the supercooled liquid region is observed in the temperature range before crystallization (T < T-x), which is different from other bulk amorphous alloys exhibiting wide supercooled liquid regions. The extremely high T-x/T-m and small Delta T-m (= T-m-T-x) values are the reason for the achievement of large glass-forming ability in this system. The bulk amorphous Pr60Fe30Al10 alloy is ferromagnetic with the Curie temperature (T-c) of 515 K which is higher than the highest T-c of 470 K for Pr-Fe binary amorphous ribbons. The remanence (B-r) and intrinsic coercive force (H-i(c)) are 0.089 T and 300 kA/m, respectively, and the crystallization to Pr+Al2Pr+delta phases causes a ferromagnetic-to-paramagnetic phase transition. Thus, the hard magnetic properties are achieved only in the amorphous state.