Chemistry Reference
In-Depth Information
Fig. 5.1
57
Fe Mössbauer
absorption spectra for (a)a
JR train ticket, and (b)a
credit card (magnetic stripe
part)
(a)
(b)
-10
-5
0
5
10
Velocity (mm/s)
helpful for readers to feel familiar with Mössbauer spectra, even if they have not
yet understood the principles of the Mössbauer effect and to get an image that the
Mössbauer spectroscopy is an easy tool. Indeed, as an analytical method, a merit of
Mössbauer spectroscopy is that we can draw out information intuitively by
glancing over the spectra.
From a viewpoint of fundamental physics, ultrathin magnetic films have been a
very interesting subject and attracted a great attention from theoretical and
experimental viewpoints. A typical example is a monolayer consisting of magnetic
atoms such as Fe or Co. However, even nowadays it is not easy to prepare a
monolayer sample of 3d elements with high crystallographic quality and also to
obtain reliable information from experimental results. A magnetic order in a two-
dimensional lattice becomes spatially unstable at elevated temperatures and
therefore relaxation phenomena are inevitably involved. There has been no con-
clusive experimental estimation concerning the Curie temperatures of Fe, Co and
Ni monolayers. Although measurements on a sample of single monolayer are
difficult, those for a multilayer sample including hundred monolayers would be
much easier. Multilayers consisting of ferromagnetic and non-magnetic layers
have been actively investigated in 1980s. If a component of multilayer is Fe or Sn,
Mössbauer spectroscopy is a powerful tool for the analysis of the magnetic
properties. If the isotope enrichment in
57
Fe is available, for instance, specified
samples for the study of monolayer magnetism are able to be prepared. Interface
properties can be investigated by preparing samples whose interfaces are selec-
tively enriched in a Mössbauer isotope.
There are two methods concerning the geometry of Mössbauer measurements:
transmission and scattering. Most Mössbauer experiments adopt a transmission
mode in which the gamma-ray from a source is counted after passing through an
absorber sample. For magnetic materials, Mössbauer measurements in transmis-
sion mode are advantageous to investigate temperature and external field depen-
dences. On the other hand, measurements in scattering mode (Conversion electron
Mössbauer spectroscopy, CEMS) are also possible by collecting the secondary
scattered
conversion
electrons.
From
transmission
and
scattering
Mössbauer
measurements,
the
same
information
is
obtained
concerning
the
hyperfine
