Magnetic properties of Nd-Fe-Co-Al rapid solidification alloys

Nd-Fe–Al–Co alloys with thickness of 0.05–4 mm were prepared by means of rapid solidification methods, suction-casting and melt-spinning, and investigated using X-ray diffraction, electron microscopy and magnetization measurements. With appropriate composition and quenching rate, the alloys behave as single-phase hard magnetic materials. Coercivity of the alloys can reach 7.6 kOe at room temperature and exceed 30 kOe at 100 K. When the thickness of the alloys is increased, multi-magnetic phase behavior is clearly performed and Nd2Fe15Al, NdAl2, Nd3Al and Nd phases are further crystallized. The optimal hard magnetic properties of the alloys closely related to a microstructure which consists of nanocrystallites with size of 10–30 nm dispersed in an amorphous matrix. The hard magnetic phase in the alloys belongs to the amorphous phase. The nanocrystallites, whose total volume fraction is very small in comparison with that of the amorphous phase, probably act as pinning centers, resulting in high coercivity behavior of the alloys.