Nanocrystallization and Recoilless Fraction Determination of Fe 68.5 Co 5 Nb 3 Cu 1 Si 15.5 B 7 Ferromagnetic Alloy
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MRS Advances © 2019 Materials Research Society DOI: 10.1557/adv.2019.34
Nanocrystallization and Recoilless Fraction Determination of Fe68.5Co5Nb3Cu1Si15.5B7 Ferromagnetic Alloy Monica Sorescu1 and Kevin Byerly2 1
Duquesne University, Department of Physics, Fisher Hall, 600 Forbes Avenue, Pittsburgh, PA 15282
2
U.S. Department of Energy, National Energy Technology Laboratory, 626 Cochrans Mill Road, Pittsburgh, PA 15236
ABSTRACT
Amorphous alloy Fe68.5Co5Nb3Cu1Si15.5B7 was obtained by melt spinning. Samples cut from the foil were annealed at 450, 550, 650 and 750 oC in a vacuum furnace. 57Fe Mӧssbauer spectroscopy was used to identify the crystalline phases formed and the orientation of the magnetic moments based on the refined values of the hyperfine parameters. The spectra of the samples annealed at 550, 650 and 750 oC were indicative of nanocrystallization, with the magnetic moments reoriented out-of-plane for the last sample. This behavior is in contradistinction to that of the Co-rich system, which was totally crystallized at these annealing temperatures. Our results show that small Co additions can lead to the formation of nanostructures over a whole range of annealing temperatures. A new series of Mӧssbauer spectra was obtained by recording simultaneously the intensity transmitted by a superposition of the sample with the stainless steel etalon, based on the dual absorber method previously introduced by us. The values of the recoilless fraction could be derived from the relative spectral areas. The f factor maintained values close to 0.7 for all samples measured, but dropped to 0.37 for the sample annealed at 750 oC. This behavior could be related to the presence of elastic stresses in the system, which caused the out-of-plane reorientation of the magnetic moment directions.
INTRODUCTION Several amorphous ferromagnetic alloy compositions have been developed in an attempt to obtain metallic glass materials with enhanced properties for a wide range of
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technological applications, from soft magnetic applications to magnetic sensors and actuators [1-7]. We can distinguish three categories of metallic glass compositions: (a) the classical metallic glasses (pre-finemet compositions), (b) the finemet compositions able to yield nanocrystalline phases upon proper annealing and (c) the advanced metallic glasses (post-finemet compositions), which will be primarily the focus of the present project. For this latest class of systems it is relevant to note that minute changes in the composition of the amorphous ferromagnetic alloys may dramatically change their properties and consequently, their applications. These additions to the composition will modify the relationship between nanocrystalline microstructure and soft magnetic properties in a predictable way. Our present study
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