NMR and Mössbauer Studies of the Amorphous System Fe79P21-xBx
Combined NMR, spin-echo and Mössbauer experiments have been performed to obtain hyperfine field distributions of the transition metal and metalloid elements in splat-cooled amorphous Fe79P21-xBx alloys. These distributions are related to the local environments of the elements. The NMR signals are observed in the low frequency range 20 – 60 MHz and all the nuclei, i.e. Fe, P and B, may contribute to the spectral distribution. The resolution of the spectra into that due to Fe and (P + B) nuclei was made possible by using samples prepared with an Fe56 isotope. The Fe distribution thus obtained shows general agreement with the Mössbauer field distribution. From a careful analysis of the NMR data, the hyperfine field at the B nuclei in these amorphous alloys is found to range from 24 to 26 KG increasing with B content. An upper limit of 8 KG for the half-width is attributed to this distribution.
The Mössbauer spectra of the Fe57 nuclei resemble those for the crystalline Fe75P25−xBx alloys. A fit of our spectra shows a field distribution which suggests the presence of structure. Such a structure may correspond to various Fe sites, also seen in the crystalline alloys. The distributions, generally lie between about 160 and 330 KG, with a maximum at about 260 KG. These spectra do not show the presence of Fe nuclei with essentially zero hyperfine field as was obtained for amorphous Fe-Pd-P by Sharon et al. and for amorphous Fe-P by Logan et al. With increasing B content the center of gravity of the Fe distribution shifts to higher values. From a systematic study of the NMR lines and other considerations it is concluded that the P field distribution is broad and its hyperfine field is between 20 and 35 KG for the higher P concentration alloys.
KeywordsField Distribution Amorphous Alloy Hyperfine Field Fe57 Nucleus Mossbauer Spectrum
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