MAGNETIC PROPERTIES OF AMORPHOUS IRON
(III) OXIDE THIN FILMS
T. Shigematsu, Yoshio Bando, T. Takada
To cite this version:
T. Shigematsu, Yoshio Bando, T. Takada. MAGNETIC PROPERTIES OF AMORPHOUS
IRON (III) OXIDE THIN FILMS. Journal de Physique Colloques, 1979, 40 (C2), pp.C2-153C2-154. <10.1051/jphyscol:1979254>. <jpa-00218652>
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Submitted on 1 Jan 1979
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Colloque Cl, supplément au n° 3, Tome 40, mars 1979, page C2-153
JOURNAL DE PHYSIQUE
MAGNETIC PROPERTIES OF AMORPHOUS IRON (ill) OXIDE THIN FILMS
T. Shigematsu, Y. Bando and T. Takada
Institute
for ChemLaal Research,
Kyoto University,
Uji, Kyoto-fu
Gil, Japan
Résumé.- Des films d'oxyde amorphe de Fe (III) ont été préparés par dépôt atomique de fer sous une
atmosphère d'oxygène de 5x10"'' torr. Les spectres Mossbauer sont un doublet paramagnétique à 300 K
et à 77 K. Les valeurs du déplacement isomérique ô et de l'effet quadrupolaire AE sont respectivement de 0,3 mm/s et 1,06 mm/s à 300 K et pour un dépôt effectué à cette température. Un champ hyperfin H de 460 kOe peut être mesuré à 4,2 K. Des valeurs de la susceptibilité magnétique, on peut
déduire une température de Néel TJJ de 48 K. On constate que H et T., sont petits et que AE est grand,
comparés aux valeurs correspondantes de Fe 2 0 3 cristallisé.
Abstract.- Amorphous iron (III) oxide films were prepared by deposition of iron metal in an oxygen
atmosphere of SxlO"1* torr. Mossbauer spectra show a paramagnetic doublet at 300 K and 77 K. The
isomer shift is 0.3 mm/s and a quadrupole splitting AE is 1.06 mm/s at 300 K for the sample obtained
at the substrate temperature of 20°C. At 4.2 K a magnetic hyperfine field was observed to be H =
460 kOe. Magnetic susceptibility measurements showed a Neel temperature T N of 48 K. In amorphous
iron (III) oxide thin films, H and TJJ become small and AE becomes large as compared with those of
crystalline Fe 2 0 3 .
Recently we have studied the preparation of
iron oxide films by reactive evaporation method /1,
0.3 mm/s relative to a-Fe and a quadrupole splitting
AE is 1.06 mm/s.
2/. We obtained the films of iron oxide such as
FejO^ and a-Pe 0, by evaporation of iron metal in
an oxygen atmosphere of pressures of 10~3 to 10 -5
torr. We have succeeded in preparing amorphous iron
oxide films with a thickness of hundreds angstrom.
In the present study, we have investigated the magnetic
properties of amorphous iron oxide films
through Mossbauer effect and magnetic susceptibility
measurements.
Experimental procedures were, for the most
part, the same as those in the previous works /1,2/.
An iron oxide film was obtained by evaporation of
iron (purity 99.9 %) in an oxygen atmosphere of pressure of 5x10 "* torr. As a substrate an acetylcellulose film was used. Iron (III) oxide films were obtained under the deposition conditions of substrate
temperature T s below 100°C and deposition rate less
than 2A/s. A film thickness was roughly 500A.
The samples prepared were examined by electron diffraction. The electron diffraction pattern
was made up of so called halos, and showed no crystalline phase.
Mossbauer spectra were measured with a con-
Fig. 1 : Mossbauer spectra of amorphous iron (III)
oxide film, T -20 (obtained at 20°C at the deposition rate 0.2 A/s).
At 4.2 K a magnetic hyperfine structure was found.
ventional spectrometer at 4.2 K, 77 K and 300 K.
From this spectrum we derive a hyperfine field
Figure 1 shows the Mossbauer spectra of the film
H = 460 kOe. Similar spectra were found on films
obtained under the deposition condition; T s = 20°C
obtained under the deposition condition; T s = 60°C
o
o
and deposition rate of 0.2A/s (referred to as Tg-20).
and deposition rate of 0.lA/s (referred to as T -60).
Mossbauer spectra show a paramagnetic doublet at
The observed Mossbauer parameters are I
77 K and 300 K. At 300 K an isomer shift I s is
and AE = 0.96 mm/s at 300 K, and H = 490 kOe at 4.2 K.
Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:1979254
= 0.3 mm/s
c2-154
JOURNAL DE PHYSIQUE
Similar Mzssbauer parameters have been observed in
From the maximum of the susceptibility the magnetic
amorphous iron (111) oxides prepared by thermal decomposition of an aerosol on a heated substrate 131
ordering temperature TN was estimated to be 48 K.
Above TN the susceptibility can be described by the
and a gel of iron oxide 141.
Magnetic susceptibility measurements were
Curie-Weiss law. The paramagnetic moment per iron
ion ueff as calculated from the slope of the reciprocal susceptibility versus temperature amounts 5.4 vB,
made between 4.2 K and 300 K with a magnetic torsion
balance. The sample for magnetic susceptibility measurement was prepared by completely dissolving the
which is close to that expected from ~e+' ions. An
asymptotic Curie temperature 0 of -95 K is derived.
acetylcellulose substrate in methyl acetate.
For the sample Ts-60, Tn was 62 K. The values of
Figure 2 shows the variation of the reciprocal susceptibility with temperature for sample Ts-20.
ueff
and 0 of Ts-60 were the same as those of Ts-20,
respectively.
The M'6ssbauer spectra and the temperature dependence of magnetic susceptibility suggest that the
amorphous iron (111) oxide films are antiferromagnetic. The Mzssbauer parameters and magnetic properties
obtained for amorphous iron (111) oxide films are
summarized in table I and compared with those for
the crystalline a-Fe,03 /5/. In the amorphous iron
(111) oxide films, H and TN become small and AE becomes large as compared with those of crystalline
a-Fe,O,. These results suggest that in the amorphous
iron (111) oxide, the number of the nearest neighbour atoms decreases, and superexchange interaction
Fig. 2 : Reciprocal susceptibility X-l versus temperature T of amorphous iron (111) oxide film, Ts-20.
was weakened due to the change of Fe-0-Fe angles and
Fe-0 distances. The difference in the values H, AE
and TN between the sample Ts-20 and Ts-60 show that
the structure in Ts-60 is closer to the crystalline
a-Fe,03 than that in Ts-20.
Table I
M'ksbauer parameters and magnetic properties of amorphous and crystalline o.-Fe203
.-
Amorphous
:
Crystalline
:
jcl-Fe20, a
:
Is : relative to cl-Fe at 300 K.
a
:
:
:
Ts-20
Ts-60
:
:
:
Sample
I
s
(mm/s)
AE
(mm/s)
:
0.3
0.3
1.06
0.96
:
0.36
0.20
AE : at 300 K.
:
H
(kOe)
I
460
490
535
TN (K)
:
:
H : measured at 4.2 K.
Cox et al. 151.
References
Bando, Y., Horii, S. and Takada, T., Japan J.
7 (1978) 1037.
Appl. Phys. 1
/2/ Shigematsu, T., Ushigome, H., Bando, Y. and
Takada, T., submitted to J. Cryst. Growth.
/I/
/3/ Van Diepen, A.M. and Pompa, Th.J.A., J. Physique
Colloq. 21 (1976) C6-755.
/ 4 / Coey, J.M.D. and Readman, P.W., Nature 246 (1973)
476.
/5/ Cox, D . E . , Shirane, G. and Ruby, S.L., Phys. Rev.
125 (1962) 1163.
.
:
48
62
:
950
:
P
p B
I
,
5.4
5.4
: