Composition dependence of the coercive force and microstructure of crystallized amorphous (FexB1-x)0.9Tb0.05La0.05alloys

Recently we showed that intrinsic coercive forces as high as 9.0 kOe with a remanent magnetization of 5 kG at room temperature could be obtained by the crystallization of the melt spun amorphous alloys (FexB1-x)0.9Tb0.05La0.05. Electron microscopy studies have shown that the observed coercive behavior results from a fine-grained (∼ 300Å or less) microstructure whose components consist mainly of the rare earth intermetallic RE6Fe23and Fe3B. In the present work we have studied the changes in magnetic properties and microstructure produced by varying the Fe/B ratio. As the iron composition x increases from 0.82 both the maximum coercive force and the remanence increase while the microstructure remains Qualitatively similar. As x decreases from 0.82 however, the maximum coercive force drops rapidly to a relatively small value. X-ray and electron microscope studies have shown that this drop in coercive force is associated with an increased amount of Fe2B and an increase in the typical grain size.