Hard magnetic properties of bulk amorphous alloys

The amorphous phase in the Nd-Fe-Al and Pr-Fe-Al systems is formed in extremely wide composition ranges of 0 to 90 at% Fe and 0 to 93 at% Al by melt spinning. Ferromagnetic Ln_90-xFe_xAl₁₀ (Ln=Nd or Pr) 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 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. Neither glass transition nor 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 ΔT_m(=T_m-T_x) values are the reason for the achievement of large glass-forming ability in these systems. The bulk amorphous Ln₆₀Fe₃₀Al₁₀ alloys are ferromagnetic with the Curie temperature (T_c) of 515 to 600 K which are much higher than those for Nd-Fe and Pr-Fe binary amorphous ribbons. The remanence (B_r) and intrinsic coercive force (_iH_c) are 0.089 to 0.122 T and 277 to 321 kA/m, respectively, and the crystallization to Ln+Al₂Ln+δ phases causes a ferromagnetic- to -paramagnetic phase transition. Thus, the hard magnetic properties are achieved only in the amorphous state.