Mössbauer Effect in Iron-Based Nanocrystalline Alloys

Abstract

Nanocrystalline ferromagnetic alloys of the Fe-Cu-Nb-B type consist of a ferromagnetic amorphous matrix in which nanograins are embedded. These nanograins normally are so small (typical diameter in the range of 5-30 nm) that, if they were free, their magnetic relaxation time would fall into the time window of the ⁵⁷Fe Mössbauer spectrometry and relaxation phenomena would become visible. It is well known that Mössbauer spetroscopy easily perceives relaxation processes on the time scale (10^-11 s to 10^-6 s). Normally the nanograins are coupled to the ferromagnetic matrix and an interaction between these two components must be regarded, too. This coupled situation influences the thermally driven fluctuation of the nanograins’ magnetization and often led to the very common interpretation of Mössbauer spectra in terms of hyperfine field distributions (also distributions of quadrupole splitting and isomer shift). Due to the high degree of complexity such spectra consist of many spectral components and an analysis becomes a rather complex task. Recently Miglierini and Greneche [1,2] proposed a new idea to interpret such hyperfine field distributions. From their paper follows that in the spectra information is available about the so-called interface between the nanograins and the residual matrix, too. Nevertheless contrary arguments (Balogh et al. [3]) and also the idea of relaxation influence on the linewidth are present in literature (Kemeny et al. [4]).