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Fig. 4.4 Theoretical
Mössbauer spectra calculated
for various relaxation times
using a discrete 2-level
relaxation model for uniaxial
symmetry: the linewidth is
0.20 mm/s, the quadrupole
shift 0.00 mm/s and the
hyperfine field ±55T. (From
[
13
])
which remains a crucial task. Indeed, the complexity of spectra might give rise to a
large number of ''mathematical'' fitting solutions but probably only a few ones are
in agreement with a physically realistic scenario. It is clear that the supporting data
established from diffraction techniques, microscopies and magnetic measurements
may discard some solutions. But
57
Fe Mössbauer experiments performed versus
temperature and/or external magnetic field are suitable to distinguish static from
dynamic effects and to see their respective evolution: thus, the physical model does
correspond to the fitting solution successfully achieved from this series of spectra.
For those reasons, the content of next sections is constrained to well charac-
terized and homogeneous nanostructured systems to illustrate the relevance but
also the limitation of by
57
Fe Mössbauer spectrometry. Consequently, it excludes
thus the use of this local spectroscopic technique to study the mechanisms asso-
ciated to thermal transformations from nanostructures into microstructures, the
growth
of
corrosive
layers
at
the
surface
of
metallic
systems submitted to
