Low temperature behavior of hyperfine fields in amorphous and nanocrystalline FeMoCuB

Abstract

Low temperature (4.2 K) magnetic behavior of Fe76Mo8Cu1B15 metallic glass was studied by 57Fe Mössbauer spectrometry (MS) and 57Fe NMR. Distributions of hyperfine magnetic fields P(B) were determined for as-quenched and annealed (nanocrystalline) samples with relative fraction of the grains about 43%. P(B) distributions were derived for both the amorphous matrix and nanocrystalline grains. NMR of alloys with natural and 57Fe enriched Fe enabled to assess the contribution of 11B to the total NMR signal. P(B) distribution of the as-quenched alloy derived from MS matches reasonably well the one from NMR of the enriched sample. NMR signal from the sample with natural Fe exhibits contributions from 11B nuclei. The principal NMR lines of the annealed alloys at 47 MHz correspond to bcc Fe nanocrystals. Small asymmetry of the lines towards higher frequencies might be an indication of possible impurity atoms in the bcc structure. The observed differences between natural and enriched samples are attributed to higher sensitivity in the latter. Positions of the lines attributed to bcc Fe nanocrystals obtained from MS and NMR are in perfect agreement.