NMR and Mössbauer Studies of the Amorphous System Fe₇₉P_21-xB_x

Abstract

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 Fe₇₉P_21-xB_x 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 Fe₇₅P_25−xB_x 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.

Supported in part by The University of Connecticut Research Foundation.

Supported by the National Science Foundation.