Chemistry Reference
In-Depth Information
12
10
8
6
4
2
0
0
5
10
15
20
t
Cr
(nm)
Fig. 5.11 Hyperfine field at the nuclear sites of atomic Sn layers doped at the center of each Cr
layer of Fe (1.0 nm)/Cr (t
Cr
) multilayers as a function of the Cr layer thickness t
Cr
magnetic hyperfine field at the Sn sites doped at the center of each Cr layer of Fe/
Cr multilayers decreases with decreasing the thickness of the Cr layer (Fig.
5.11
).
This result indicates that the magnetic moments of Cr in Fe/Cr multilayers reduce
as the thickness of the Cr layer decreases [
21
]. Such kind of information on
antiferromagnets cannot be obtained by other experimental methods.
5.6.3 Sn-Containing Ferromagnetic Alloy Films
In some Sn-containing ferromagnetic alloys and compounds,
119
Sn Mössbauer
spectra can be an informative tool to investigate the magnetism. A representative
intermetallic alloy is Co
2
MnSn, which is one of the Heusler compounds having an
L2
1-
type ordered crystallographic structure. Co
2
MnSn is expected to have high
conduction-electron spin polarization (so-called half metallic), which is a hot topic
in the field of ''spintronics''. This is actually an old material and Mössbauer spectra
for bulk Co
2
MnSn have been published by several groups. However, it is not easy to
prepare alloys with a highly ordered structure and obtain a Mössbauer spectrum with
a single Sn environment. Recently, thin films of this alloy have been prepared using
atomically controlled alternate deposition to see the possibility of improving the
local environments of the constituent atoms [
22
]. Figure
5.12
shows the Mössbauer
spectra and corresponding distribution of hyperfine field for bulk Co
2
MnSn
prepared by arc-melting and a Co
2
MnSn films prepared by atomically controlled
alternate deposition. The former spectrum was measured by a transmission method
and the latter by a CEMS method. It is clear that the sample prepared by arc-melting
has two prominent peaks in the hyperfine distribution suggesting that there are two
environments in the Sn sites, whereas the film sample prepared by atomically
controlled distribution has almost one [
22
]. Using such Co
2
MnSn films with rela-
tively uniform local environments, studies on interface magnetism of Heusler alloy
films, especially its temperature dependence, are now in progress.
