Magnetic properties and transmission electron microscopy microstructures of exchange coupled Nd12-xFe82+xB6 melt spun ribbons

The nanocomposite melt spun ribbons of the alloys Nd12-xFe82+xB6 (x=O, 2.5, 3, and 4) have been prepared by rapid quenching and/or post heat treatment. In the alloy with x=O, homogeneous grain morphologies were obtained at the lower wheel speed (18 m/s less than or equal to Sw less than or equal to 25 m/s) to result in a strong exchange coupling effect between Nd2Fe14B and alpha-Fe grains, the magnetic properties of Br=9.6 kG, iHc=7.7 kOe, and (BH)max=18 MGOe was achieved. In the alloys with x=2.5, 3, and 4, exchange coupling effect is also found and the best magnetic properties of Br=11.4 kG, iHc=6.3 kOe, and (BH)max=19 MGOe are achieved in the alloy ribbons with x=2.5 quenched at a wheel speed of 18 mis without any post heat treatment. Inasmuch as the crystallization temperature of the ribbons increased with decreasing the Nd content, the microstructures, the size and volume fraction of the alpha-Fe and Nd2Fe14B phases evaluated by transmission electron microscopy observation, of the above alloy ribbons were dominated by the Nd content, the wheel speed and the heat treatment temperature apparently. As a result, the exchange coupling effect and the magnetic properties of the ribbons were strongly affected. (C) 1996 American Institute of Physics.