Local Structure and Thermal Relaxation in Metallic Glasses

An analytic formula of the Mossbauer absorption spectrum of iron-containing magnetic metallic glasses is presented. Analytic relationships between the parameters of their Mossbauer spectra and of the local fields of the 57Fe nucli are derived. The inverse relationship between the absorption line widths and line amplitudes for the absorption lines i and 7-i (i = 1 to 3), observed in many magnetic metallic glasses, is obtained. The asymmetric Mossbauer spectrum of these amorphous alloy is found to be the result of the correlation of the distribution of the magnetic fields with that of the quadrupole fields (EFGs) and/or of the isomer shifts. Thermal structure relaxation of magnetic metallic glasses Fe40Ni40P14B6 was studied using 57Fe Mossbauer effect. We found that during the thermal relaxation processes of this amorphous alloy, there exist amorphous clustered subunits that re-adjust their relative position to lower the energy of the system and thereby voids between these structure subunits are annealed out resulting in the irreversible thermal relaxation we oberved. The amorphous clustered model is then, among the proposed models, most suitable for describing the local structure of this amorphous alloy. Sub-Tg thermal relaxation of a-Fe40Ni40P14B6 was also studied by room temperature Mossbauer effect. We found this sub-Tg relaxation results in the re-orientation of its internal magnetic field. Both linear and nonlinear relaxation, that can be associated with the relaxation phenomena of system not far from and far from thermodynamic equilibrium, respectively, was observed. Evidences are presented to show that the magnetic field re-orientation we observed is truly a relaxation phenomena in contrast with the observation of the magnetic field re-orientation due to the surface crystallization after the sample been annealed at high temperature for a long time.