“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.