In this work, we have studied the effects of the coaddition of Al(1.5 at. %)/Ge(1 at. %) and heat-treatment temperature on the structure and magnetic properties of rapidly quenched pure Fe73.5-xSi13.5B9Nb3Cu (FINEMET) alloys prepared by the single roller melt spinning process. Two series of as-spun and heat-treated alloys, 400, 480, 560, 640, and 730 degrees C for 1 h in vacuum (10(-6) Torr), were studied using various techniques such as x-ray diffraction (XRD), transmission electron microscopy (TEM), differential scanning calorimetry (DSC), Mossbauer spectroscopy, and B-H loop tracer. Mossbauer analysis carried out on both series of alloys heat treated at 560 degrees C revealed the presence of two phases, Fe3Si phase with D0(3) structure and a residual amorphous phase with reduced hyperfine field (16.9 T) compared to those of Al/Ge added (22.5 T) and pure FINEMET (similar to 23.4 T) alloys, in close agreement with XRD and TEM results. The highest maximum permeability, saturation magnetization, and the lowest coercivity were obtained for both series of alloys when heat treated at 560 degrees C. However, the magnitude of coercivity was lower for the Al/Ge substituted alloy (heat treated at 560 degrees C) compared to that of the pure FINEMET alloy. This is due to the substitution of Al atoms for Fe as confirmed by our XRD and Mossbauer results. Further, a higher ferromagnetic amorphous phase Curie temperature (T-C,T-am) was detected for the Al/Ge added alloy (322 degrees C) compared to that of the pure FINEMET alloy (317 degrees C), which is believed to be mainly related to the presence of Ge atoms in the amorphous matrix. Furthermore, the removal of stress and the setup of nanocrystallization for both series of alloys gave rise to a higher collinear magnetic moment angle. However, this was not the case for the samples heat treated at temperatures above 560 degrees C, for which the formation of the Fe-B hard magnetic phase was confirmed by our XRD, TEM, and Mossbauer results. Finally, the structural-magnetic properties relationship is discussed for various samples studied in this work.
2007. Vol. 76, no 2, 024434- p.