Transcript Shinjo_Multilayers.ppt

Mössbauer spectroscopic
studies by T.SHINJO
Degree of interlayer mixing is different at the two interfaces (head and
tail). A result for Fe layer in contact with Mn layer is shown here.
Sample A is prepared by depositing
Sample
56Fe(100Å)-57Fe(3.5Å)-Mn(100Å).
structure
While B is prepared by depositing
Mn(100Å)-57Fe(3.5Å)-56Fe(100Å)
A shows the situation of Mn-on-Fe,
While B shows Fe-on-Mn.
Spectra
Spectrum for A is entirely ferromagnetic
at RT
but that for B includes a large non-magn
fraction. The result means that the mixin
Sample A is limited but a considerable
mixing happened in Sample B.
Such a phenomenon occurs generally
if one component is rather reactive.
Spectra of ultrathin Fe layers sandwiched in MgF2
The thinnest layer (Fe16Å) shows a decrease of hyperfine field at RT
and an increase at 4K
T.Shinjo et al..
Proc.Inter.Vac.Cong.
(Vienne,1977)
Mössbauer spectra for Fe/Mg multilayers
Crystalline
---------------
measured at 4K.
Sample structure is [Fe(a Å)/Mg(b Å)]x50.
a is from 1Å to 30Å (as indicated in the figure)
while b is always 20Å ～30Å
Amorphous
Results
1)
Fe monoatomic layer is entirely
ferromagnetic 4K.
2)
Magnetization is oriented perpendicular to the
film in the monolayer region and turned out to b
in-plane for a > 10Å .
3)
Structure of Fe layer is crystalline for a >15Å
but amorphous-like for a < 12Å
K.Kawaguchi et al. J.Phys.Soc.Jpn.55(1986)2375. .
.
Mössbauer spectra at 4K of Fe/rare-earth multilayers.
Perpendicular magnetization appears for Pr,Nd and Tb.
y
K.Mibu and T.Shinjo, Hyper.Int. 113(1998)287.
Evidence of Fe5+
Charge disproportionation
of Fe in CaFeO3,
2Fe4+ ↔ Fe3+ + Fe5+.
Temp.dep.of the
difference of IS(↑),
and hyperfine field(←).
At 110K ～285K
At RT, a single line is observed, which
corresponds to Fe4+. Below 280K, two
isomer shifts are observed, due to the
charge disproportionation.
At 4K, with
and
without
48kOe
T.Shinjo et al. Ferrites, Proc.Int.Conf.Japan(1980)
Magnetic order appears below 110K
and 2 different hyperfine fields are
observed at 4K. The larger one,
415kOe is close to the typical value for
Fe3+. Therefore the other is attributed
to Fe5+.
The spectrum with applying 48kOe
suggests a non-collinear spin structure.
Mössbauer spectrum of natural Fe
at ultralow temperature (5 milli-Kelvin)
Intensity of P1 is usually equal to that of P6, At normal temperatures, the levels A and B
are equally distributed since the energy separation by the hyperfine field, 34T, is only
2mK. At ultralow temperatures, however, the Boltzmann population deviates from
equal (nuclear polarization）..
P1
P6
A
B
Mössbauer spectrum of a natural iron foil at extremely low temperature.
The asymmetry of the 6-line is caused by the nuclear polarization at the ultralow temperature and P6/P1
indicates the relative populations at level B and A, which is determined by Hn/kT. Since the hyperfine
field is 34T, the temperature can be estimated to be 5mK.
T,Shinjo, Hyper.Int.42(1988)1173.