Mössbauer spectroscopic studies by T.SHINJO. Degree of interlayer mixing is different at the two...
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Transcript of Mössbauer spectroscopic studies by T.SHINJO. Degree of interlayer mixing is different at the two...
“Gütlich, Bill, Trautwein: Mössbauer Spectroscopy and Transition Metal Chemistry@Springer-Verlag 2009”
Mössbauer spectroscopic studies by T.SHINJO
“Gütlich, Bill, Trautwein: Mössbauer Spectroscopy and Transition Metal Chemistry@Springer-Verlag 2009”
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
56Fe(100Å)-57Fe(3.5Å)-Mn(100Å).
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.
Spectrum for A is entirely ferromagnetic
but that for B includes a large non-magnetic
fraction. The result means that the mixing in
Sample A is limited but a considerable
mixing happened in Sample B.
Such a phenomenon occurs generally
if one component is rather reactive.
Sample
structure
Spectra
at RT
“Gütlich, Bill, Trautwein: Mössbauer Spectroscopy and Transition Metal Chemistry@Springer-Verlag 2009”
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)
“Gütlich, Bill, Trautwein: Mössbauer Spectroscopy and Transition Metal Chemistry@Springer-Verlag 2009”
Crystalline
---------------
Amorphous
Mössbauer spectra for Fe/Mg multilayers
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
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 be
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. .
.
“Gütlich, Bill, Trautwein: Mössbauer Spectroscopy and Transition Metal Chemistry@Springer-Verlag 2009”
y
Mössbauer spectra at 4K of Fe/rare-earth multilayers.
Perpendicular magnetization appears for Pr,Nd and Tb.
K.Mibu and T.Shinjo, Hyper.Int. 113(1998)287.
“Gütlich, Bill, Trautwein: Mössbauer Spectroscopy and Transition Metal Chemistry@Springer-Verlag 2009”
Evidence of Fe5+
Charge disproportionation of
Fe in CaFeO3,
2Fe4+ ↔ Fe3+ + Fe5+.
At 110K ~ 285K
At 4K, with and without 48kOe
Temp.dep.of the
difference of IS(↑),
and hyperfine field(←).
At RT, a single line is observed, which corresponds to Fe4+. Below 280K, two isomer shifts are observed, due to the charge disproportionation.
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.
T.Shinjo et al. Ferrites, Proc.Int.Conf.Japan(1980)
“Gütlich, Bill, Trautwein: Mössbauer Spectroscopy and Transition Metal Chemistry@Springer-Verlag 2009”
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
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.
Mössbauer spectrum of a natural iron foil at extremely low temperature.