Nobuyasu Adachi,KazuhiroIsarai,
セラミックス基盤工学研究センター年報(2010).
Vol. 10,1-4Toshitaka Ota, Kazushi Ishiyama, Hiroyasu Ota, Kenichi Arai

論文

Synthesis of Completely Substituted Bi3Fe5O12 Garnet Films
by Metal Organic Deposition Technique(New Preparation Technique of Completely Substituted Bismuth Garnet Films)
Nobuyasu Adachi, Kazuhiro Isarai, Toshitaka Ota, Kazushi Ishiyama*,
Hiroyasu Ota**, Kenichi Arai***
Ceramics Research Laboratory, Nagoya Institute of Technology, 10-6-29 Asahigaoka, Tajimi, Gifu 507-0071 JAPAN*Tohoku University, Sendai Reserch Center, 2-1-1 Katahira, Aoba-ku, Sendai 980-8577, JAPAN**National Institute of Information and Communications Technology, 6-6-3 Minamiyoshinari, Aoba-ku, Sendai, JAPAN***Research Institute for Electric and Magnetic Materials, 2-1-1 Yagiyamaminami, Taihaku-ku, Sendai 982-0807, JAPANThermally non equilibrium garnet Bi3Fe5O12 was prepared by metal organic decomposition (MOD) technique and the magnetooptical properties were investigated for the magneto-optical (MO) imaging. The spin-coating process on the Gd3Ga5O12 (100)substrate was repeated 5 times and the thickness was approximately 150 nm. The garnet phase was epitaxially crystallized on thesingle crystal substrate at the annealing temperatures of 500 and 550℃ and the lattice constant of the garnet film was estimatedto be 12.64 Å. The saturation magnetization was estimated to be 1.67 kgauss and the maximum Faraday rotation at the wavelengthof 635 nm showed 6.7 degree/mm. High performance of the MO properties can be expected to be the probe sensor of highfrequency electromagnetic field with high spatial resolution.
Keywords: completely substituted bismuth iron garnet, MOD technique, magneto-optics, in-plane anisotropythere is no flux with low melting point below 600 ℃ at
the present stage. Recently, the highly Bi substituted
garnet films prepared by liquid phase such as metalorganic decomposition (MOD) techniques have beenstudied and the real time observations of the magnetic
flux distribution in superconducting materials havealready been achieved4),10),11). In this paper, we report thesynthesis of thermally non equilibrium materials fromthe liquid phase using MOD technique and show thehigh performance of MO effect of the film with thethickness of nanometer order.

1. IntroductionCompletely substituted bismuth iron garnet film
(Bi3Fe5O12: BIG) has the largest magneto-optical (MO)effect in infrared and visible light region among thegarnet materials, however, that material is thermally nonequilibrium system. Since the first successful synthesisof BIG by the reactive ion beam sputtering (RIBS)
technique1), much attention of this material has been
attracted for the application in nonreciprocal waveguidedevices, waveguide optical isolators, MO imaging ofsuperconducting materials2),4) and recently, MO
imagings of high frequency electromagnetic field5),6).
The growth techniques of BIG films have been mainly
studied by vapor phase depositions such as electron
cyclotron resonance (ECR) sputtering, RF sputteringand pulsed laser deposition (PLD)7)-9), whereas, thosetechniques often induced 3-dimensional (3D) island
growth or misfit dislocations which prevents opticallysmooth surface of the films. In order to realize the flat
surface of the film, the growth from the liquid phase hasa great advantage. The liquid phase epitaxy technique ispractically used as a commercial technique for opticalisolators of the Bi substituted garnet materials; however,2. Experiments

The precursor of BIG films were prepared by spincoating of a metal-organic solution (molar ratio Bi : Fe
=3 : 5, Kojundo Chemical Lab. Co.) The total
concentration of Bi and Fe carboxylate in the metalorganic solution was fixed to 3 %. The metal-organicsolution was spin-coated on Gd3Ga5O12 (100) single
crystal substrate (lattice parameter as = 12.373 Å) at
3000 rpm for 30 seconds. In comparison with (111)substrate, (100) substrate is easier to grow the film withmagnetic easy axis parallel to the film plane because―1―Synthesis of Completely Substituted Bi3Fe5O12 Garnet Films by Metal Organic Deposition Technique<111> axis is the magnetic easy axis of the garnet
crystal. The film with magnetic easy axis parallel to thefilm plane is necessary for the high resolution MO
imaging 3. The substrates were 1 inch diameter and 0.5mm thick. After drying at 100 ℃ for 30 minutes in anoven, the films were pre-annealed at 400 ℃ for 30
minutes in order to decompose the metal-organicsolution. These processes were repeated 5 times. Then,the substrate was cut into approximately 5 × 5 mm2 andthe amorphous films placed on Pt plate were annealed ininfrared furnace for 3 hours at 450 500, 550 600 and650 ℃, respectively. All annealing treatments wereachieved in an air atmosphere. The crystalline analysisof annealed films was performed by X-ray diffraction(XRD) technique (Rigaku RINT1000). The thicknessesof the films were estimated by the cross section
observations by the scanning electron microscopy(JEOL: JSM-7000FO). The magnetic properties were
measured by SQUID magnetometer (Quantum Design
MPMS 7). The Faraday rotation was measured by using
the MO spectrometer (JASCO K-250). The
measurements of magnetizations and MO properties
were performed at room temperature.

℃. Since the bismuth is volatile, the change of thecomposition ratio of Bi: Fe was checked before and after
annealing process. A few milliliters of MOD liquids
were placed in an alumina crucible and they wereannealed at 400, 550, and 700 ℃, respectively. The
precipitate was dissolved in heated nitric acid. As aresult of the Inductively Coupled Plasma (ICP) analysis
shown in Table I, no change of the composition ratio wasconfirmed before and after annealing the MOD liquids.
The composition ratio of Bi: Fe of the annealed spincoated films are also considered to be 3：5.
Table I. ICP analysis of the annealed MOD liquid

The XRD spectra of the film annealed between 400
and 650 ℃ are shown in Fig.2. At the annealing
temperatures below 450 ℃, no diffraction peaks fromthe films were observed. The (00l) diffraction peaks ofthe garnet phase appeared for the film annealed at 500
and 550 ℃. This indicates that the garnet phase wasepitaxially crystallized from the amorphous phase in thetemperature range between 500 and 550 ℃. Those (00l)peaks disappear for the films annealed above 600 ℃.

3. Results and Discussions

Differential thermal analysis showed that the metalorganic solution was decomposed through 2 steps asshown in Fig. 1. The organic solvent was evaporated
near the temperature of 100 ℃ and the exothermic DTA
peaks appeared around 290 ℃ and 400 ℃ indicates thedecompositions of metal organic compounds through 2steps. The temperature of the pre-annealing of the films
was adjusted to the upper reaction temperature of 400

Fig.2. XRD q-2q scans in CuKa radiation for pre-annealed andFig. 1. DTA curve of MO solution (molar ration of Bi : Fe = 3

annealed films on GGG (100) substrates grown by MOD: 5).

technique.
―2―Nobuyasu Adachi, Kazuhiro Isarai, Toshitaka Ota, Kazushi Ishiyama, Hiroyasu Ota, Kenichi Arai

Since BIG phase is thermally non-equilibrium, thegarnet phase of the film was considered to bedecomposed due to the high temperature.
The lattice parameter a0 of the films was deduced byplotting a0 against the Nelson-Riley function12):the film annealed at 500 ℃, respectively. Taking into
account the experimental errors, the lattice parametersof the films prepared by the MOD technique can beregarded to be the same with the films prepared by vapor
phase depositions5).
The optimum annealing temperature has beenconcluded to be around 550 ℃ by Faraday rotation
measurements. The film annealed at 550 ℃ indicates alarger MO effect than the film annealed at 500 ℃. TheFaraday hysteresis loops at 635 nm are shown in Fig.4.
The maximum Faraday rotation of the film annealed at550 ℃ reached approximately 1°. The annealing
temperature of 550 ℃ is the same as the optimum
deposition temperature of the BIG films prepared by thePLD technique9). The magnetizations per unit volume
and the Faraday rotations per unit length are calculated
by using the thickness value of 150 nm estimated fromthe scanning electron microprobe (SEM) observations.
Strictly speaking, the raw data of the magnetization andthe Faraday rotation include the components of theparamagnetic GGG substrate. The paramagnetism of thesubstrate dominates the raw magnetization data. For theMO effect, the Faraday rotation due to the magnetic
garnet dominates the raw data, however, those values are
not negligible for the case of the very thin films withnanometer thickness. As both the magnetization and theFaraday rotation of the substrate increase linearly withincreasing the magnetic field, it is possible to separate
the component of the film from the draw data by
subtractive calculations of the substrate components.
The calculated magnetic hysteresis loop per unit volume
and the Faraday rotation hysteresis per unit length are(1)Fig.3. Lattice parameters for films annealed at 500 ℃ (symbols○ ) and 550 ℃ (symbols ● ) techniques. Lattice parameter acosq

was calculated from (004), (008), (0012), and (0016) Braggreflections position. Experimental acosq vs. q dependence has been
fitted to Nelson-Riley equation (1) to extrapolate at cosq → 0.

where acosq is an interplane distance calculated from theapparent Bragg peak position at 2q and K is a fitting
coefficient. Fig. 3 presents the lattice parameters acosqcalculated from (004), (008), (0012) Bragg reflections
for the films. The “true” lattice parameters a0, obtained
as an extrapolation of cos2q to 0, were found to be
12.635 Å for the film annealed at 550 ℃, 12.634 Å for

Fig.5. Magnetizations of the film per unit volume in themagnetic field parallel to the film plane (solid line) and the
Faraday rotation qF vs. H ⊥ at 635 nm per unit length (symbols
Fig.4. Faraday rotation qF vs. H ⊥ at 635 nm of the film plus the● ). Paramagnetic contribution from GGG substrate has beenGGG substrate.

subtracted.
―3―Synthesis of Completely Substituted Bi3Fe5O12 Garnet Films by Metal Organic Deposition Technique

thank to staff members of Institute of Molecular Sciencefor SQUID measurements. The authors would also likethan to Professor Ishibashi (Nagaoka UniversityofTechnology) for useful discussions.

shown in Fig.5. The magnetization easily saturates forthe case of the applied magnetic field parallel to the film
plane, which indicates the in-plane magnetic anisotropy.
The Faraday rotation saturate at approximately 2 kOe.
The saturation magnetization of the film was deduced tobe approximately 1.7 kgauss and the maximum Faraday
rotation shows a large performance of 6.7°/mm at 635
nm. In order to visualize a distribution of high frequency
electromagnetic field on integrated circuits, a highspatial resolution is necessary for the MOI probe. The
high performance of MO effect of BIG film may enablehigh resolution observations of the order of 1
micrometer. Enough Faraday rotation can be expected
for the BIG thin film of the thickness less than 1
micrometer and the spatial resolution can be reduced tothe order of the visible light wavelength. In addition,
simple spin coating method will be also expected for theapplicationof
magnetophotonic
crystalwith13),14)
multilayered structure
because a spin coatingprocess is possible to control the nanometer thickness ofthe film and easy to change the composition of the layerat each coating.

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4. Conclusions

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Single crystal Bi3Fe5O12 (100) films have beensuccessfully synthesized on GGG (100) substrates by
MOD technique. The amorphous phase of the spincoated film was crystallized to the garnet phase at theannealing temperature of 500 ℃ and 550 ℃. For thefilm annealed at 550 ℃, the saturation magnetizationand the maximum Faraday rotation at 635 nm are 1.7
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Acknowledgements

Nishimura, Springer Series in Materials Science 94

This work was supported by the Strategic Information
and Communications R&D Promotion Programme(SCOPE) of Ministry of Internal Affairs andCommunications of Japan.. The authors would like

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