Thermomagnetic monitoring of nanocomposite formation in mechanically alloyed Nd-Fe-B alloys

A mechanical alloying technique was applied to NdxFe94-xB6 (x = 5.5-11.0) alloys for preparing an exchange-coupled nanocomposite. The structural development during the nanocomposite formation was monitored by thermomagnetic means. The mechanically alloyed NdxFe94-xB6 alloys in the as-milled condition consisted of an amorphous Nd-Fe-B phase and alpha-Fe nanocrystallites. The crystallisation temperature of the amorphous phase was independent of the milling time. The amorphous phase in the as-milled NdxFe94-xB6 alloys with higher Nd content had a lower crystallisation temperature. The NdxFe94-xB6 (x = 8.5) alloy milled for longer than 30 h consisted of a two-phase structure containing alpha-Fe and NdxFe94-xB6 phases after being isothermally annealed at 600 degreesC for 20 min. This annealed powder showed a smooth demagnetisation curve, indicating an intergranular exchange coupling between the hard Nd2Fe14B and soft magnetic alpha-Fe grains. (C) 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.