Recent advances in the development of (Fe,Co)(88)M7B4Cu1 magnets (invited)

Annealing of amorphous precursor alloys, with compositions (Fe,Co)(88)M7B4C u1 (M=Zr, Nb, Hf), above their primary crystallization temperature results in the nanocrystallization of the ferromagnetic alpha'-FeCo phase. This wor k describes results of the characterization of these alloys, including morp hological and chemical stability of the alpha'-FeCo phase, examination of a lloy compositions, and development of a pseudo-Slater-Pauling curve for the amorphous precursor alloys. Samples with the composition Fe44Co44Zr7B4Cu1 were annealed at 600 degrees C for 10, 31, 100, 308, 1000, and 3072 h in Ar and examined by x-ray diffraction (XRD) and transmission electron microsco py (TEM). Scherrer analysis of x-ray peak breadths was used to infer only a slight increase in the grain size of the sample annealed for 3072 h (simil ar to 60 nm) compared to the samples annealed for short times (similar to 4 0 nm). TEM studies revealed a distribution of grain sizes in the material w ith an average grain size of 42 nm for the 3072 h annealed sample. Samples annealed at higher temperatures exhibited the additional minority phases (F e,Co)(3)Zr and ZrO. XRD analysis of the samples annealed for extended times at 600 degrees C do not indicate any formation of these phases, even in th e sample annealed for 3072 h. TEM indicates the formation of minority phase s, probably resulting from the devitrification of the amorphous grain-bound ary phase and/or oxidation upon extended annealing. Differential scanning c alorimetry results on alloys of composition (Fe0.5Co0.5)(89)Zr7B4 and (Fe0. 65Co0.35)(88)Zr7B4Cu1 show primary crystallization temperatures of 495 and 480 degrees C, respectively. (C) 2000 American Institute of Physics. [S0021 -8979(00)77508-6].