Synthesis of glassy Fe-Co-Nd-Zr-B alloys and their crystallization-induced magnetic properties

A new Fe-based amorphous alloy exhibiting the glass transition and supercooled liquid region before crystallization was searched in the composition range of Fe₆₃Co₇Nd_10-x-Zr_xB₂₀ (x=0 to 6 at%). The amorphous alloys containing 4 to 6 at%Zr were found to exhibit the glass transition, followed by a supercooled liquid region. The crystallization from the supercooled liquid of the 4%Zr alloy occurred through three stages of Am-→Am′+Fe₃B→Am″+Fe₃B+γ-Fe+ Nd₂Fe₂₃B₃+Fe₂Zr+Fe ₃Zr→α-Fe+Fe₂Zr+Fe₃Zr+Nd ₂Fe₁₄B+Fe₂B+ZrB₂. In the crystallized state, the 4% and 6%Zr alloys exhibited hard magnetic properties, i.e., saturation magnetization of 1.15 to 1.18 T, remanence of 0.75 to 0.76 T, coercive force of 30 to 58 kA/m and maximum energy product of 7.8 to 13 kJ/m³. The grain sizes of the α-Fe and Nd₂Fe₁₄B phases for the 4%Zr alloy subjected to optimum annealing were about 45 and 25 nm, respectively. The fine mixed structure was thought to reveal the hard magnetic properties by the exchange magnetic coupling mechanism even in the coexistent state with Fe₂Zr, Fe₃Zr, Fe₂B and ZrB₂. The appearance of the glass transition also implies that the 4%Zr and 6%Zr alloys have a high glass-forming ability leading to the formation of a bulk amorphous alloy. The finding that the amorphous alloys exhibited the glass transition in the as-quenched state and the hard magnetic properties in the crystallized state is important, because the direct production of a bulk hard magnetic alloy by a simple process is expected, such as the crystallization of the cast bulk amorphous alloy.