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Submitted on 1 Jan 1979
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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.C2-153-C2-154.
�10.1051/jphyscol:1979254�. �jpa-00218652�
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
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 TN 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 Fe203.
Recently we have studied the preparation of iron oxide films by reactive evaporation method / 1 , 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 mag- netic 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 pres- sure of 5x10 "* torr. As a substrate an acetylcellu- lose film was used. Iron (III) oxide films were ob- tained under the deposition conditions of substrate temperature Ts below 100°C and deposition rate less than 2A/s. A film thickness was roughly 500A.
The samples prepared were examined by elec- tron diffraction. The electron diffraction pattern was made up of so called halos, and showed no crys-
talline phase.
Mossbauer spectra were measured with a con- ventional spectrometer at 4.2 K, 77 K and 300 K.
Figure 1 shows the Mossbauer spectra of the film obtained under the deposition condition; Ts = 20°C
o
and deposition rate of 0.2A/s (referred to as Tg-20).
Mossbauer spectra show a paramagnetic doublet at 77 K and 300 K. At 300 K an isomer shift Is is
0.3 mm/s relative to a-Fe and a quadrupole splitting AE is 1.06 mm/s.
At 4.2 K a magnetic hyperfine structure was found.
From this spectrum we derive a hyperfine field H = 460 kOe. Similar spectra were found on films obtained under the deposition condition; Ts = 60°C
o
and deposition rate of 0.lA/s (referred to as T -60).
The observed Mossbauer parameters are I = 0.3 mm/s and AE = 0.96 mm/s at 300 K, and H = 490 kOe at 4.2 K.
Fig. 1 : Mossbauer spectra of amorphous iron (III) oxide film, T -20 (obtained at 20°C at the deposi- tion rate 0.2 A/s).
JOURNAL DE PHYSIQUE
Colloque Cl, supplément au n° 3, Tome 40, mars 1979, page C2-153
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 respective- ment de 0,3 mm/s et 1,06 mm/s à 300 K et pour un dépôt effectué à cette température. Un champ hyper- fin 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 Fe203 cristallisé.
Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:1979254
c2-
154 JOURNAL DE PHYSIQUE Similar Mzssbauer parameters have been observed inamorphous iron (111) oxides prepared by thermal de- composition of an aerosol on a heated substrate 131 and a gel of iron oxide 141.
Magnetic susceptibility measurements were made between 4.2 K and 300 K with a magnetic torsion balance. The sample for magnetic susceptibility mea- surement was prepared by completely dissolving the acetylcellulose substrate in methyl acetate.
Figure 2 shows the variation of the recipro- cal susceptibility with temperature for sample Ts-20.
Fig. 2 : Reciprocal susceptibility X-l versus tempe- rature T of amorphous iron (111) oxide film, Ts-20.
From the maximum of the susceptibility the magnetic ordering temperature TN was estimated to be 48 K.
Above TN the susceptibility can be described by the Curie-Weiss law. The paramagnetic moment per iron ion
ueff
as calculated from the slope of the recipro- cal susceptibility versus temperature amounts 5.4 vB, which is close to that expected from ~e+' ions. Anasymptotic Curie temperature 0 of -95 K is derived.
For the sample Ts-60, Tn was 62 K. The values of
ueff
and 0 of Ts-60 were the same as those of Ts-20, respectively.The M'6ssbauer spectra and the temperature de- pendence of magnetic susceptibility suggest that the amorphous iron (111) oxide films are antiferromagne- tic. 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 T become small and AE be- N
comes 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 neigh- bour atoms decreases, and superexchange interaction was weakened due to the change of Fe-0-Fe angles and Fe-0 distances. The difference in the values H, AE and T between the sample Ts-20 and Ts-60 show that
N
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
.-
: Sample : I s AE H
I
TN (K) P p BI
.
,-
: (mm/s) : (mm/s) : (kOe) :: Ts-20 : 0.3 1.06 : 460 48 : 5.4 :
Amorphous
: Ts-60 0.3 0.96 490 62 : 5.4
: Crystalline jcl-Fe20, a : 0.36 0.20 535 : 950 :
Is : relative to cl-Fe at 300 K. AE : at 300 K. H : measured at 4.2 K.
a : Cox et al. 151.
References
/ I / Bando, Y., Horii, S. and Takada, T., Japan J.
Appl. Phys.
17
(1978) 1037./2/ Shigematsu, T., Ushigome, H., Bando, Y. and Takada, T., submitted to J. Cryst. Growth.
/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.
