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Optics Express

Optics Express

  • Editor: C. Martijn de Sterke
  • Vol. 20, Iss. 9 — Apr. 23, 2012
  • pp: 9624–9639
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Giant Faraday rotation in BixCe3-xFe5O12 epitaxial garnet films

M. Chandra Sekhar, Mahi R. Singh, Shantanu Basu, and Sai Pinnepalli  »View Author Affiliations


Optics Express, Vol. 20, Issue 9, pp. 9624-9639 (2012)
http://dx.doi.org/10.1364/OE.20.009624


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Abstract

Thin films of BixCe3-xFe5O12 with x = 0.7 and 0.8 compositions were prepared by using pulsed laser deposition. We investigated the effects of processing parameters used to fabricate these films by measuring various physical properties such as X-ray diffraction, transmittance, magnetization and Faraday rotation. In this study, we propose a phase diagram which provides a suitable window for the deposition of BixCe3-xFe5O12 epitaxial films. We have also observed a giant Faraday rotation of 1-1.10 degree/µm in our optimized films. The measured Faraday rotation value is 1.6 and 50 times larger than that of CeYIG and YIG respectively. A theoretical model has been proposed for Faraday rotation based on density matrix method and an excellent agreement between experiment and theory is found.

© 2012 OSA

1. Introduction

There is a considerable interest in the study of Faraday rotation in garnet thin films at communication wavelengths [1

1. M. Levy, “The on-chip integration of magnetooptic waveguide isolators,” IEEE J. Sel. Top. Quantum Electron. 8(6), 1300–1306 (2002). [CrossRef]

24

24. L. Bi, J. Hu, P. Jiang, D. H. Kim, G. F. Dionne, L. C. Kimerling, and C. A. Ross, “On chip optical isolation in monolithically integrated non-reciprocal optical resonators,” Nat. Photonics 5(12), 758–762 (2011). [CrossRef]

]. High transmittance, low optical absorption and high Faraday rotation are key properties that make garnet materials as a suitable candidate for integrated optics [1

1. M. Levy, “The on-chip integration of magnetooptic waveguide isolators,” IEEE J. Sel. Top. Quantum Electron. 8(6), 1300–1306 (2002). [CrossRef]

4

4. Z. C. Xu, “Magnetooptic caracteristiques of BiTbGaIG film/TbYbBiIG bulk crystal composite structure in 1550 nm band,” Appl. Phys. Lett. 89(3), 032501 (2006). [CrossRef]

]. It is known that the Faraday rotation in garnet materials is studied using transmission geometry. In this method, the garnet materials are magnetized along the direction of the light propagation and the final output of the light is not similar as the original input; instead it rotates two times the Faraday rotation angle. In double pass geometry, light is reflected from a dielectric mirror behind the film and passes twice through the magneto optical medium [2

2. A. K. Zvezdin and V. A. Kotov, Modern magneto-optics and magneto optical materials, (IOP publishing, Bristol, 1997).

]. Thus, the property of non reciprocity has an immense technological importance and can be exploited to produce fundamental optical components such as rotators, and isolators [1

1. M. Levy, “The on-chip integration of magnetooptic waveguide isolators,” IEEE J. Sel. Top. Quantum Electron. 8(6), 1300–1306 (2002). [CrossRef]

,2

2. A. K. Zvezdin and V. A. Kotov, Modern magneto-optics and magneto optical materials, (IOP publishing, Bristol, 1997).

]. Garnet materials with extremely high Faraday rotation are required for the miniaturization of optical isolator devices. Cerium and bismuth substituted iron garnet materials have a wide range of applications including magneto optical devices and magneto photonic crystals [1

1. M. Levy, “The on-chip integration of magnetooptic waveguide isolators,” IEEE J. Sel. Top. Quantum Electron. 8(6), 1300–1306 (2002). [CrossRef]

20

20. M. Chandra Sekhar, J. Y. Hwang, M. Ferrera, Y. Linzon, L. Razzari, C. Harnagea, M. Zaezjev, A. Pignolet, and R. Morandotti, “Strong enhancement of the Faraday rotation in Ce and Bi comodified epitaxial iron garnet thin films,” Appl. Phys. Lett. 94(18), 181916 (2009). [CrossRef]

]. The performance of these devices depends strongly on the physical properties of garnets, such as magnetization, transmittance, Verdet constant and Faraday rotation. Magneto optical properties of a garnet material also depend on the preparative conditions which can be controlled or by proper substitution of various lanthanide elements [3

3. S. Kahl, S. I. Khartsev, A. M. Grishin, K. Kawano, G. Kong, R. A. Chakalov, and J. S. Abell, “Structure, microstructure, and magneto-optical properties of laser deposited Bi3Fe5O12/Gd3Ga5O12 (111) films,” J. Appl. Phys. 91(12), 9556–9560 (2002). [CrossRef]

].

Faraday rotation of pure and doped yttrium iron garnet materials depend on the selection of suitable substrates as well as doping of the lanthanide elements. In garnet thin films, the choice of substrate plays a key role in determining the films magneto optical properties (i.e. Faraday rotation) and minimization of losses associated with absorption [18

18. T. Körner, A. Heinrich, M. Weckerle, P. Roocks, and B. Strizker, “Integration of magneto-optical active bismuth iron garnet on nongarnet substrates,” J. Appl. Phys. 103(7), 07B337 (2008). [CrossRef]

]. Several garnet materials, such as certain lanthanide- doped yttrium iron garnet (YIG) materials, have been proposed to improve Faraday rotation [19

19. J. Ostorero and M. Guillot, “Magneto-optical properties of Sc-substituted dysprosium iron garnet single crystals,” J. Appl. Phys. 91(10), 7296–7298 (2002). [CrossRef]

21

21. J. Y. Hwang, R. Morandotti, and A. Pignolet, “Strong Faraday rotation in Ce and Bi comodified epitaxial iron garnet films: valence control through strain engineering,” Appl. Phys. Lett. 99(5), 051916 (2011). [CrossRef]

] at the telecom wavelength 1.55µm. Despite their ability to exhibit a high degree of Faraday rotation, the YIG and other doped materials have severe transmission losses and other compatibility issues with optical integration schemes. The integration of optical isolators and other issues are mentioned in the following.

Optical isolators are bulky and require expensive optics and alignment. Integration of these devices and other non reciprocal devices on a single chip is challenging. The magneto optical materials cannot be implemented as a wave guide core layers on semiconductor wafers due to lower refractive index. Another difficulty arises due to the phase velocity mismatch inherent in the waveguide geometry (structural birefringence). These problems can be minimized by using III-V semiconductor with a non reciprocal and reciprocal mode converter in an asymmetric waveguide, which will avoid mode matching problems [22

22. B. M. Holmes and D. C. Hutchings, “Demonstration of quasi-phase-matched nonreciprocal polarization rotation in III-V semiconductor waveguides incorporating magneto-optic upper claddings,” Appl. Phys. Lett. 88(6), 061116 (2006). [CrossRef]

]. The non reciprocal mode converter is formed from a III-V semiconductor waveguide core with a magneto optic layer as the upper cladding material so that the Faraday rotation occurs through the interaction of the evanescent tail of a guided mode. The phase velocity mismatch due to the waveguide birefringence can be prevented using a quasi-phase-matching approach [22

22. B. M. Holmes and D. C. Hutchings, “Demonstration of quasi-phase-matched nonreciprocal polarization rotation in III-V semiconductor waveguides incorporating magneto-optic upper claddings,” Appl. Phys. Lett. 88(6), 061116 (2006). [CrossRef]

]. However, this solution may complicate the fabrication process.

In another report [23

23. Z. Yu and S. Fan, “Complete optical isolation created by indirect interband photonic transitions,” Nat. Photonics 3(2), 91–94 (2009). [CrossRef]

], it was explained about non linear optical processes in magneto optical devices such as electro-optic modulators where the isolation occurs at specific power levels only [23

23. Z. Yu and S. Fan, “Complete optical isolation created by indirect interband photonic transitions,” Nat. Photonics 3(2), 91–94 (2009). [CrossRef]

]. To circumvent this problem, it was reported in the literature [23

23. Z. Yu and S. Fan, “Complete optical isolation created by indirect interband photonic transitions,” Nat. Photonics 3(2), 91–94 (2009). [CrossRef]

] that non reciprocal (complete) isolation can be achieved by spatial and temporal refractive index modulations where photon states can go through interband transitions similar to the electronic transition in semiconductors. Most importantly, this method of modulation has no impact on the backward propagation of light. These structures can absorb incident light traveling in one direction while transmitting light in the opposite direction; in this way the method of isolation is achieved [23

23. Z. Yu and S. Fan, “Complete optical isolation created by indirect interband photonic transitions,” Nat. Photonics 3(2), 91–94 (2009). [CrossRef]

]. Recently, this concept was demonstrated on monolithic integration of isolators with a foot length of 290 µm fabricated on a cerium doped yttrium iron garnet material using YIG buffer layer on an SOI platform [24

24. L. Bi, J. Hu, P. Jiang, D. H. Kim, G. F. Dionne, L. C. Kimerling, and C. A. Ross, “On chip optical isolation in monolithically integrated non-reciprocal optical resonators,” Nat. Photonics 5(12), 758–762 (2011). [CrossRef]

, 25

25. J. Fujita, M. Levy, R. M. Osgood Jr, L. Wilkens, and H. Dotsch, “Waveguide optical isolator based on Mach-Zehnder interferometer,” Appl. Phys. Lett. 76(16), 2158 (2000). [CrossRef]

].

Another approach to optical integration which has been intensively explored using waveguide –isolators, which involve nonreciprocal phase shifts as a “blocking” mechanism, have been intensively explored [26

26. T. Mizumoto, K. Oochi, T. Harada, and Y. Naito, “Measurement of optical nonreciprocal phase shift in a Bi-substituted Gd3Fe5O12 film and application to waveguide-type optical circulator,” J. Lightwave Technol. 4(3), 347–352 (1986). [CrossRef]

30

30. Y. Shoji, T. Mizumoto, H. Yokoi, I. W. Hsieh, and R. M. Osgood Jr., “Magneto optical isolator with silicon waveguides fabricated by direct bonding,” Appl. Phys. Lett. 92(7), 071117 (2008). [CrossRef]

]. This arrangement usually employed in a Mach-Zehnder interferometer (MZI) configuration with nonreciprocal and reciprocal phase shifters as both active and passive components [26

26. T. Mizumoto, K. Oochi, T. Harada, and Y. Naito, “Measurement of optical nonreciprocal phase shift in a Bi-substituted Gd3Fe5O12 film and application to waveguide-type optical circulator,” J. Lightwave Technol. 4(3), 347–352 (1986). [CrossRef]

30

30. Y. Shoji, T. Mizumoto, H. Yokoi, I. W. Hsieh, and R. M. Osgood Jr., “Magneto optical isolator with silicon waveguides fabricated by direct bonding,” Appl. Phys. Lett. 92(7), 071117 (2008). [CrossRef]

]. The waveguide –isolator approach is appealing because it is less sensitive to fabrication errors and there is no need for phase matching between orthogonally polarized modes. To produce an optical isolator with complete isolation, it is necessary to minimize all the problems mentioned above. This requires keeping both the active and passive isolator components on a single platform.

In our investigation, considerable effort has been placed in the development of new magneto optical materials with controlled processing parameters such as temperature and pressure. The aim of this research is to produce new bismuth-cerium iron garnet BixCe3-xFe5O12 films that exhibit higher transmittance and giant Faraday rotation at communication wavelengths. We synthesized several batches of BixCe3-xFe5O12 films on gadolinium and gallium garnet substrates using the pulsed laser deposition. The advantage of using this deposition is the transfer of the target stoichiometry to the film [31

31. D. B. Chrisey and G. K. Hubler, Pulsed Laser Deposition of thin films (Wiley Interscience, 1994).

37

37. W. K. Lee, H. Y. Wong, K. Y. Chan, T. K. Yong, S. S. Yap, and T. Y. Tou, “Effects of laser fluence on the structural properties of pulsed laser deposited ruthenium thin films” Appl. Phys. A. Mater. Sci. Process. 100(2), 561–568 (2010). [CrossRef]

]. In the fabrication of these films, we investigated the role of processing parameters such as distance between the laser beam and the target, laser fluency, partial pressure of gases, temperature, and choice of substrate. We found that all of the above processing parameters play a prominent role in influencing the degree of Faraday rotation. Furthermore, we proposed a phase diagram for the processing parameters which can be used in the fabrication of these epitaxial thin films. This phase diagram provides detailed knowledge in achieving a giant Faraday rotation in garnet thin films. We show that BixCe3-xFe5O12 epitaxial films can be used to fabricate optical isolators with a dimension of 45µm. This is an important device that can be used to protect from unwanted reflected light that causes noise and instability in the laser system.

2. Experimental results and data analysis

We prepared BixCe3-xFe5O12 material with stoichiometric ratios with x = 0.7 and 0.8 and which were sent to praxair-USA for the preparation of dense-ceramic targets with a material purity of 99.99%. After receiving the right stoichiometry of BixCe3-xFe5O12, target was ablated with a pulsed excimer KrF laser (λ=248 nm) in the pulsed laser deposition chamber. The laser was set with a repetition rate of 20 Hz and focused onto the target. We used a Gd3Ga5O12 substrate in the fabrication of all epitaxial thin films. The choice of this material as a substrate was driven by the need to minimize both the lattice parameter and thermal expansion mismatch to enable epitaxial growth. We took precautions to avoid any strain and cracking in the film that arises due to thermal expansion mismatch between the film and the substrate [3

3. S. Kahl, S. I. Khartsev, A. M. Grishin, K. Kawano, G. Kong, R. A. Chakalov, and J. S. Abell, “Structure, microstructure, and magneto-optical properties of laser deposited Bi3Fe5O12/Gd3Ga5O12 (111) films,” J. Appl. Phys. 91(12), 9556–9560 (2002). [CrossRef]

, 6

6. G. B. Scott and D. E. Lacklison, “Magnetooptic properties and applications of bismuth substituted iron garnets,” IEEE Trans. Magn. 12(4), 292–311 (1976). [CrossRef]

, 10

10. Y. H. Kim, J. S. Kim, S. I. Kim, and M. Levy, “Epitaxial growth and properties of Bi-substituted yttrium-iron garnet films grown on (111) gadolinium-gallium-garnet substrates by using rf magnetron sputtering,” J. Korean Phys. Soc. 43(3), 400–405 (2003).

, 11

11. S. I. Khartsev and A. M. Grishin, “[Bi3Fe5O12/Gd3Ga5O12] magneto-optical photonic crystals,” Appl. Phys. Lett. 87(12), 122504 (2005). [CrossRef]

, 14

14. T. Shintaku, A. Tate, and S. Mino, “Ce-substituted yttrium iron garnet films prepared on Gd3Sc2Ga3O12 garnet substrates by sputter epitaxy,” Appl. Phys. Lett. 71(12), 1640–1642 (1997). [CrossRef]

, 21

21. J. Y. Hwang, R. Morandotti, and A. Pignolet, “Strong Faraday rotation in Ce and Bi comodified epitaxial iron garnet films: valence control through strain engineering,” Appl. Phys. Lett. 99(5), 051916 (2011). [CrossRef]

, 22

22. B. M. Holmes and D. C. Hutchings, “Demonstration of quasi-phase-matched nonreciprocal polarization rotation in III-V semiconductor waveguides incorporating magneto-optic upper claddings,” Appl. Phys. Lett. 88(6), 061116 (2006). [CrossRef]

] in order to obtain smooth deposition of these films. To circumvent the misfit dislocations which are caused by lattice parameter mismatch between the film and substrate, which would worsen the film properties [20

20. M. Chandra Sekhar, J. Y. Hwang, M. Ferrera, Y. Linzon, L. Razzari, C. Harnagea, M. Zaezjev, A. Pignolet, and R. Morandotti, “Strong enhancement of the Faraday rotation in Ce and Bi comodified epitaxial iron garnet thin films,” Appl. Phys. Lett. 94(18), 181916 (2009). [CrossRef]

, 34

34. M. Chandrasekhar, “Structural and dielectric properties of Ba0.5Sr0.5TiO3 thin films grown on LAO with homo-epitaxial layer for tunable applications,” Int. J. Mod. Phys. B 18(15), 2153–2168 (2004). [CrossRef]

36

36. M. Zaezjev, M. Chandrasekhar, M. Ferrera, L. Razzari, A. Pignolet, R. Morandotti, B. Holmes, M. Sorel, and D. Hutchings, “Effect of the Foreign Phases on the crystallization and Growth of Magnetooptic garnet Films, in conference on Lasers and Electro-Optics/Quantum Electronics and Laser science Conference and Photonic Applications Systems Technologies, OSA technical digest (CD) (Optical Society of America, 2008) paper CThM5.

], we chose gadolinium and gallium garnet substrate for the deposition of the BixCe3-xFe5O12 epitaxial films. In the deposition of these epitaxial films, the substrate to film lattice mismatch is about 1.9% which can be calculated from the lattice constants of all these garnets (yttrium iron garnet =12.377Å, Gd3Ga5O12 =12.378Å and Bi3Fe5O12 =12.63 Å). The thermal expansion mismatch is below 10% (thermal expansion constants: yttrium iron garnet = 10.4 x 10−6/°C, Gd3Ga5O12=9.2x 10−6/°C). In addition, this substrate has an excellent transparency and low contribution to the Faraday rotation (0.002deg/μm) [20

20. M. Chandra Sekhar, J. Y. Hwang, M. Ferrera, Y. Linzon, L. Razzari, C. Harnagea, M. Zaezjev, A. Pignolet, and R. Morandotti, “Strong enhancement of the Faraday rotation in Ce and Bi comodified epitaxial iron garnet thin films,” Appl. Phys. Lett. 94(18), 181916 (2009). [CrossRef]

, 38

38. S. Kang, S. Yin, V. Adyam, Q. Li, and Y. Zhu, “Bi3Fe4Ga1O12 Garnet properties and its application to ultrafast switching in the visible spectrum,” IEEE Trans. Magn. 43(9), 3656–3660 (2007). [CrossRef]

].

Before the deposition, the substrate was heated to 500°C for thermal cleaning of the surface. For the depositing the films on the substrate background gasses (such as oxygen, argon, and argon + hydrogen) are introduced in the deposition chamber separately. The interaction of the gases with the target produces the molecular species such as cerium and bismuth and further helps in the formation of proper crystalline phase [3

3. S. Kahl, S. I. Khartsev, A. M. Grishin, K. Kawano, G. Kong, R. A. Chakalov, and J. S. Abell, “Structure, microstructure, and magneto-optical properties of laser deposited Bi3Fe5O12/Gd3Ga5O12 (111) films,” J. Appl. Phys. 91(12), 9556–9560 (2002). [CrossRef]

, 10

10. Y. H. Kim, J. S. Kim, S. I. Kim, and M. Levy, “Epitaxial growth and properties of Bi-substituted yttrium-iron garnet films grown on (111) gadolinium-gallium-garnet substrates by using rf magnetron sputtering,” J. Korean Phys. Soc. 43(3), 400–405 (2003).

, 11

11. S. I. Khartsev and A. M. Grishin, “[Bi3Fe5O12/Gd3Ga5O12] magneto-optical photonic crystals,” Appl. Phys. Lett. 87(12), 122504 (2005). [CrossRef]

, 14

14. T. Shintaku, A. Tate, and S. Mino, “Ce-substituted yttrium iron garnet films prepared on Gd3Sc2Ga3O12 garnet substrates by sputter epitaxy,” Appl. Phys. Lett. 71(12), 1640–1642 (1997). [CrossRef]

, 21

21. J. Y. Hwang, R. Morandotti, and A. Pignolet, “Strong Faraday rotation in Ce and Bi comodified epitaxial iron garnet films: valence control through strain engineering,” Appl. Phys. Lett. 99(5), 051916 (2011). [CrossRef]

, 22

22. B. M. Holmes and D. C. Hutchings, “Demonstration of quasi-phase-matched nonreciprocal polarization rotation in III-V semiconductor waveguides incorporating magneto-optic upper claddings,” Appl. Phys. Lett. 88(6), 061116 (2006). [CrossRef]

]. Introduction of the gases further reduce the kinetic energy of the molecular species (impinging particles) on the substrate and the growing film.

In the deposition of films, we used three gases, namely oxygen, reduced atmosphere and argon and varied the pressure of these gases in the range of (50-500 m.Torr). After film deposition using pulsed laser deposition, the ramping process was completed in three stages. In the first step, the samples were cooled at a rate of 10°C/min until the temperature reached 400°C. In the second stage, the samples were maintained at this temperature for 40 minutes of in situ annealing. In the last stage, the temperature was reduced to room temperature at the same cooling rate as in the first step. We found a deposition rate of 0.25-0.36 nm/sec to achieve 0.9-1 μm thick BixCe3-xFe5O12 epitaxial films.

2.1 Optimization of process parameters in fabricating BixCe3-xFe5O12 epitaxial films

After gradual increase in the partial pressure of reduced atmosphere (Ar + H2), in the range of 200-350 m.Torr and using similar temperatures, we found a cubic structure and high Faraday rotation. Further increase in partial pressures of reduced atmosphere (Ar + H2), resulted in black color samples which exhibited poor transmittance.

2.2 X-ray diffraction

X-ray diffraction measurements were carried out using Xpert panalytical (Philips) 3373/10 diffractometer attached with a copper Cu-Kα radiation source (with a λ Cu-Kα = 1.54056 Ǻ MRD) operating at 45 kV and 40 mA in a θ-2θ arrangement. Figure 3
Fig. 3 a) Out of plane-X-ray diffraction of BixCe3-xFe5O12 epitaxial (x = 0.7) film and inset showing the rocking scan of the film b) In plane X –ray diffraction pattern of BixCe3-xFe5O12 (x = 0.7) epitaxial layer scan (top) c) GGG substrate (640) reflection scan.
shows details of the X- ray diffraction for both out of plane (θ-2θ) and in plane (Φ) patterns of BixCe3-xFe5O12 epitaxial films. We obtained similar diffraction patterns for both the compositions (x = 0.7, 0.8) studied here.

Figure 3 shows crystallographic structure of BixCe3-xFe5O12 epitaxial films. The θ-2θ scan shows only reflections from the planes which are integer multiples of the 111 plane, proving that the film is only (111) oriented in the growth direction.

The broadened XRD (444) film peak and Gd3Ga5O12 substrate peaks (444) are clearly defined with X-ray diffraction measurements. The lattice constants of (111) oriented BixCe3-xFe5O12 epitaxial films were found to be 12.47Å for film and 12.42 Å for GGG. The BixCe3-xFe5O12 epitaxial films and GGG substrate have the full width at half maximum of 0.2 and 0.020 respectively (Fig. 3). In every BixCe3-xFe5O12 film structural analysis, no other crystalline material other than BiCeIG phase was observed. Further to prove cube on cube relationship, we extended our measurements to scan in plane (ϕ-scan) orientation of the samples. Figure 3(a) represents the ϕ-scan of the 640 reflections of the film and gadolinium and gallium garnet substrate. Basically, this analysis gives information about azimuthal orientation of the grains in the film plane. Therefore, the ϕ-scan of the BixCe3-xFe5O12 (640) reflection displays six equally spaced peaks (six-fold symmetry) at the similar angles for the film and the substrate, suggesting that the film is epitaxial and properly oriented in the substrate plane. This was also confirmed with other in plane orientations such as (642) and (420) which were performed on these films to ensure their structural symmetry. From Fig. 3, it is clear that these films crystallize in a cubic –pervoskite type structure. The structures of these BixCe3-xFe5O12 materials depend on the magnetic anisotropy and magnetization of the material, the sample shape, defects, the temperature, surface treatment, and the history of the sample [17

17. D. C. Hutchings, “Prospects for the implementation of magneto-optic elements in optoelectronic integrated circuits: a personal perspective,” J. Phys. D. 36(18), 2222–2229 (2003). [CrossRef]

]. Bismuth was used to enhance the lattice constant of the films over that of the gadolinium and gallium garnet substrate so that films were in compression state as evident from X-ray diffraction measurements. After verifying the structure in these compositions, it is important to determine the passage of light through these samples by studying the transmittance measurements.

2.3 Transmittance

The transmittance spectrums of BixCe3-xFe5O12 epitaxial films were obtained using ultraviolet-visible spectrophotometer in the range of 190-2000 nm with a resolution wavelength of 1nm. Figure 4
Fig. 4 Transmittance spectrum is plotted as a function of wavelength for BixCe3-xFe5O12 films a) x = 0.8 b) x = 0.7) films at a partial pressure of 300 m.Torr argon.
shows the transmittance spectrum as a function of the wavelength for garnet epitaxial films. We measured the transmittance as a function of wavelength at an argon partial pressure of 300 m.Torr. We observed the transmittance up to 62% for x = 0.7 and 80% for x = 0.8 epitaxial films. The increased transmittance for x = 0.8 composition may be attributed to the importance of processing parameters especially temperature and partial pressure of argon. Using other partial pressures (oxygen and reduced atmosphere) for the deposition of films, we found a decreased transmittance due to porosity that may affect the propagation of light due to scattering. We have also observed slightly lower Faraday rotation in x = 0.7 composition in comparison with the x = 0.8 composition. The oscillation in Fig. 4 (a) are attribute to theelectron transitions from 5d excited level to the 4f ground state of Ce3+ (2F5/2, 2F7/2) [2

2. A. K. Zvezdin and V. A. Kotov, Modern magneto-optics and magneto optical materials, (IOP publishing, Bristol, 1997).

]. The absorption edge for both of the compositions is observed between 370 and 420 nm. Furthermore, absorption decreases with an increase in transmittance at infrared wavelengths (>1600 nm) and garnet materials become fully transparent.

2.4 Morphology and topographical studies

The scanning electron microscope (SEM) images were obtained with JEOL-JSM, for BixCe3-xFe5O12 epitaxial films. The SEM is used for viewing topological (surface), morphological (bulk-structure) and grain distribution at high magnifications. The accelerating voltage was varied from 0.2 to 5 KV in 0.1 increments and from 5 to 30 kV in 1 kV increments. The basic SEM is connected to an energy dispersive X-ray analysis unit, which displays the characteristic X-ray spectrum. The images were collected on both the compositions and are displayed in Fig. 5
Fig. 5 a) Cross sectional scanning electron microscope (SEM) image of BixCe3-xFe5O12 epitaxial film (x = 0.7). Note that its thickness is marked at the interface. b) Scanning electron microscope (SEM) image of BixCe3-xFe5O12 epitaxial film (x = 0.8) c) AFM topography of the BixCe3-xFe5O12 (x = 0.7) epitaxial film d) AFM topography of the BixCe3-xFe5O12 (x = 0.8) epitaxial film e) AFM roughness details of the epitaxial (x = 0.8) film. All the films were treated in argon 300 m. torr.
. To measure the surface roughness of the films Atomic Force Microscope (AFM) was employed using a Veeco enviroscope equipped with Co/Cr coated cantilevers (NSC 36) from MicroMasch. We employed thetapping mode to collect images of the surface topography. In this mode, the cantilever oscillation amplitude of the AFM is kept constant by a feedback loop. When the tip attached to the cantilever passes over a surface of the sample, the cantilever oscillates at its resonance. The amplitude of the cantilever tends to change according to the surface features. Finally, these amplitude variations are used to identify the surface profile (imaging). Figure. 5 show details on SEM and AFM topography of BixCe3-xFe5O12 epitaxial films.

We measured the thickness of the BixCe3-xFe5O12 epitaxial films from the cross sectional SEM image and stylus profilometer. From the cross sectional image, we found a thickness of 1 μm for the BixCe3-xFe5O12 films and this thickness is in agreement with the one measured from profilometer within the error of ± 0.5%. We also measured the thickness of the films from ellipsometric data for all these garnet films and found similar agreement when in comparison with the above measurements. The grain distribution was found to be dense without any cracks observed from SEM images, as shown in Fig. 5(b). The topographic nature of BixCe3-xFe5O12 epitaxial films are shown in AFM Figs. 5(c)-5(e). From these measurements, we found that the lateral dimension of the grain varies from 110 to 200 nm for films deposited at temperatures 690-700°C. We evaluated the root mean square (rms) surface roughness for all films over areas of 2 x 2μm2 from the AFM measurements. These values are in the range of 1.3-2.6 nm. The dimensions and topographic features are similar in all the films studied. The Faraday rotation is strongly influenced by the film topography due to surface roughness. The decrease in roughness parameter relates to the improvement with the film epitaxy which is also supported by X-ray diffraction observation.

2.5 Magnetization

The magnetization measurements of the samples were made using Superconducting Quantum Interference Device (SQUID). The system employs a probe located in a helium gas exchange cryostat for measuring the field dependence of magnetization. The system is equipped with a DC magnet for fields up to 50 Gauss. The cryostat is surrounded by a µ-metal shield, which keeps the remnant field up to 20 milli-Guass. Figure 6
Fig. 6 Magnetization dependence on temperature of the BixCe3-xFe5O12 (x = 0.8) epitaxial film. The inset shows the inverse susceptibility as a function of temperature and its Curie-Weiss dependence.
displays magnetization behaviour of the BixCe3-xFe5O12 epitaxial films. The magnetic field was applied in the film plane. Both the electron spin and the orbital angular momentum contribute to the magnetization which leads to a positive susceptibility. To obtain the exact magnetic susceptibility of the film, the substrate paramagnetic susceptibility has been removed [39

39. S. Geller and M. A. Gilleo, “The crystal structure and ferrimagnetism of yttrium–iron garnet Y3Fe2(FeO4)3,” J. Phys. Chem. Solids 3(1–2), 30–36 (1957). [CrossRef]

]. After correcting the magnetization data, the obtained spectra for

BixCe3-xFe5O12 epitaxial films from SQUID consist of paramagnetic type transition. In these measurements; we did not observe any loop in the BixCe3-xFe5O12 spectrums that show a clear signature of paramagnetic type transition. Another evidence for paramagnetism is shown in the inset of Fig. 6(b), where the variation of inverse susceptibility with temperature follows a Curie-Weiss law with a linear dependence in a broad temperature range. It is also known that yttrium iron garnet has a ferrimagnetic structure with Curie temperature of 500-600 K [39

39. S. Geller and M. A. Gilleo, “The crystal structure and ferrimagnetism of yttrium–iron garnet Y3Fe2(FeO4)3,” J. Phys. Chem. Solids 3(1–2), 30–36 (1957). [CrossRef]

]. In pure yttrium iron garnet at a specific substitution level, both the tetrahedral and octahedral sublattices are equivalent and they compensate each other. Hence, in this case magnetization is one of the dodecahedral substituting ion/ions [39

39. S. Geller and M. A. Gilleo, “The crystal structure and ferrimagnetism of yttrium–iron garnet Y3Fe2(FeO4)3,” J. Phys. Chem. Solids 3(1–2), 30–36 (1957). [CrossRef]

]. Similarly, magnetization spectra were obtained for BixCe3-xFe5O12 epitaxial films with other treatments and compositions using argon, implying that these samples were displaying paramagnetic type in the entire temperature range studied. These results are very promising for developing a magneto optical device. Further processing features identified in this investigation are presented in the following section.

2.6 Phase diagram

In this study the repeated measurements are very important to know the overall magneto optical response of the films and to determine the optimized window for several physical properties associated in achieving a giant Faraday rotation. The phase diagramclearly explains the efforts in producing excellent epitaxial BixCe3-xFe5O12 films with a narrow window (rectangle-region) of deposition. We also confirmed that argon pressure between 200 and 375 m.Torr and the temperature 690-720°C is the main influencing parameters in depositing these epitaxial films on GGG substrates.

2.7 Faraday rotation

We designed an optical setup with the magnet supplied by GMW-USA for measuring Faraday rotation @ 1.55 µm wavelengths. The sample was placed between the two poles of an electromagnet and an optical beam from a laser diode, with wavelength λ= 1550 nm was transmitted through the sample, parallel to the magnetic field axis. In our experiments, a quarter wave plate and a polarizer facilitated the scan of all the possible input linear polarization states. A polarizing beam splitter was used to collect the sample output intensities of the two polarization components, parallel (p-component) and orthogonal (s-component) to the propagation plane. The differential signal, chopped at 1.5 kHz, is obtained from two photodiodes connected to the Lock-in amplifier. When a magnetic field is applied, a polarization rotation is induced in the magneto optical material and the powers of the ‘s’ and ‘p’ components are different resulting in a “nonzero” differential signal recorded by the lock-in amplifier.

The differential arrangement has been chosen because it allows for a 3dB signal to noise ratio increment with respect to the one-channel detection. In this experiment, Lock-in integration times exceeding 1000 chopping cycle periods were adopted to remove the background noise.

Figure 8
Fig. 8 The Faraday rotation is plotted as a function of magnetic field -B (Tesla) for BixCe3-xFe5O12 epitaxial films (x = 0.8). Samples are treated in an argon (300 m.Torr) pressure. The experimental data are represented with open diamonds, (measured with GMW-USA magnet) and the solid line represents the theoretical calculation based on the density matrix method. Inset shows the paramagnetic –spectral transitions.
shows the Faraday rotation measurements on our 1μm BixCe3-xFe5O12 thick sample and the rotation 1.00 & 1.10 degree/µm has been recorded together with a saturation field of 0.5 Tesla. Note that these values are 1.6 times higher than the existing cerium doped yttrium iron garnet and 50 times higher than pure yttrium iron garnet materials.

In the following, we present a theory on Faraday rotation using the density matrix method [40

40. M. O. Scully and M. S. Zubary, Quantum optics, (Cambridge University Press, 1997).

] to correlate with experiment. It is considered that the BixCe3-xFe5O12 sample contains N (number density) per unit volume, and an external laser field with frequency ωρ and amplitude Ερ is propagating in the sample. Note that the garnet material considered here exhibits paramagnetic behavior. Therefore, the electronic transitions which are responsible for the Faraday rotation in the presence of magnetic field B, denoted as 1S0(ML=0)P31(ML=1) and 1S0(ML=0)P31(ML=1) [2

2. A. K. Zvezdin and V. A. Kotov, Modern magneto-optics and magneto optical materials, (IOP publishing, Bristol, 1997).

, 6

6. G. B. Scott and D. E. Lacklison, “Magnetooptic properties and applications of bismuth substituted iron garnets,” IEEE Trans. Magn. 12(4), 292–311 (1976). [CrossRef]

]. The energy levels S10(ML=0),P31(ML=1)and P31(ML=1)are denoted as |1,|2and |3respectively. The levels for states |1,|2and |3 have energies ε1,ε2 and ε3 respectively. The energy difference between ε2 and ε3 is ε2ε3 = (ħeB)/m* where, e and m* are the charge and the effective mass of the charge carriers, respectively.

ΘF=ωpL4ncRe(χ+χ)
(2)

Expressions for susceptibility χ± can be written in terms of the density matrix element as
χ+=N2n2(μ21ρ21Ep) (2-a)
χ=N2n2(μ31ρ31Ep) (2-b)
where ρ21 and ρ13 are the density matrix elements for the transitions |2|1 and |1|3 respectively. Similarly, μ12and μ13 are induced dipole moments because of transitions |2|1 and|1|3.

Using density matrix method for the three level model given in the inset of Fig. 8 and using Eqs. (1-2), we obtained the following expression for the Faraday rotation after rigorous mathematical treatment:
ΘF=(NωpL16cn3)Re(i(ρ3ρ1)μ221d12i(ρ2ρ1)μ312d13d13d12)
(3)
where d12=γ12+i(ωp(ε2ε1)) and d13=γ13+i(ωp(ε3ε1)). The parametersγ12 and γ13 are spontaneous decay rates of the transitions 1S0(ML=0)P31(ML=1)and 1S0(ML=0)P31(ML=1) respectively. The parameter ρi(I = 1, 2, 3) and ρi=[e(εiεF)/kBT+1]1 are the Fermi distribution function denoted for |ith energy state.

Numerical calculations were performed for the Faraday rotation using Eq. (3) with MAPLE software. The parameters appearing in this theory are taken from reference [2

2. A. K. Zvezdin and V. A. Kotov, Modern magneto-optics and magneto optical materials, (IOP publishing, Bristol, 1997).

]. Only the optimal parameter N was used in fitting, since we do not know the N (number density) of the present materials. The numerical calculations are plotted in Fig. 8 along with experimental data. Note we find an excellent agreement between theory and experiment. Based on our extensive characterization of these epitaxial films, we believe that the major contribution to the Faraday rotation enhancement comes from an increase in the concentration of Ce3+ induced by the substitution of Bi3+. Detailed calculations on Monte-Carlo methods using X-ray photoelectron spectroscopy are in progress.

3. Conclusions

Acknowledgments

MCS thanks the Institute de la National Recherché Scientifique, QC for using some of the facilities. Thanks to Stefan Lauroche, Ecole de Polytechnique, QC for useful discussions on transmittance measurements. Authors thank Joel Cox for editing the manuscript. Also, MCS thanks, Brain Richter GMW –Associates USA for valuable tips to setup the magneto optical measurements.

References and links

1.

M. Levy, “The on-chip integration of magnetooptic waveguide isolators,” IEEE J. Sel. Top. Quantum Electron. 8(6), 1300–1306 (2002). [CrossRef]

2.

A. K. Zvezdin and V. A. Kotov, Modern magneto-optics and magneto optical materials, (IOP publishing, Bristol, 1997).

3.

S. Kahl, S. I. Khartsev, A. M. Grishin, K. Kawano, G. Kong, R. A. Chakalov, and J. S. Abell, “Structure, microstructure, and magneto-optical properties of laser deposited Bi3Fe5O12/Gd3Ga5O12 (111) films,” J. Appl. Phys. 91(12), 9556–9560 (2002). [CrossRef]

4.

Z. C. Xu, “Magnetooptic caracteristiques of BiTbGaIG film/TbYbBiIG bulk crystal composite structure in 1550 nm band,” Appl. Phys. Lett. 89(3), 032501 (2006). [CrossRef]

5.

R. G. David, Fiber Optic Reference Guide, 3rd ed. (Boston Focal Press, 2002), p. 5.

6.

G. B. Scott and D. E. Lacklison, “Magnetooptic properties and applications of bismuth substituted iron garnets,” IEEE Trans. Magn. 12(4), 292–311 (1976). [CrossRef]

7.

T. Okuda, N. Koshizuka, K. Hayashi, T. Takahashi, H. Kotani, and H. Yamamoto, “Epitaxial growth of Bi-substituted yttrium iron garnet films by ion beam sputtering,” Advances in magneto-optics, Proceedings. Int. Symp. Magneto-optics, J. Magn. Soc. Jpn. 11, Supplement S1, 179–182 (1987).

8.

B. Teggart, R. Atkinson, and I. W. Salter, “Enhancement of the polar Kerr effect in bismuth-substituted DyGa iron garnet thin films,” J. Phys. D Appl. Phys. 31(19), 2442–2446 (1998). [CrossRef]

9.

M. Inoue, K. Arai, T. Fuji, and M. Abe, “One-dimensional magneto photonic crystals,” J. Appl. Phys. 85(8), 5768–5770 (1999). [CrossRef]

10.

Y. H. Kim, J. S. Kim, S. I. Kim, and M. Levy, “Epitaxial growth and properties of Bi-substituted yttrium-iron garnet films grown on (111) gadolinium-gallium-garnet substrates by using rf magnetron sputtering,” J. Korean Phys. Soc. 43(3), 400–405 (2003).

11.

S. I. Khartsev and A. M. Grishin, “[Bi3Fe5O12/Gd3Ga5O12] magneto-optical photonic crystals,” Appl. Phys. Lett. 87(12), 122504 (2005). [CrossRef]

12.

R. Lux, A. Heinrich, S. Leitenmeier, T. Korner, M. Herbort, and B. Stritzker, “Pulsed-laser deposition and growth studies of Bi3Fe5O12 thin films,” J. Appl. Phys. 100(11), 113511 (2006). [CrossRef]

13.

M. Vasiliev, K. E. Alameh, V. A. Kotov, and Y. T. Lee, “ Nanostructured engineered materials with high magneto-optic performance for integrated photonics applications,” in Proceedings. IEEE Photonics Global @Singapore, (IPGC 2008).

14.

T. Shintaku, A. Tate, and S. Mino, “Ce-substituted yttrium iron garnet films prepared on Gd3Sc2Ga3O12 garnet substrates by sputter epitaxy,” Appl. Phys. Lett. 71(12), 1640–1642 (1997). [CrossRef]

15.

L. Bi, H. S. Kim, G. F. Dionne, S. A. Speakman, D. Bono, and C. A. Ross, “Structural, magnetic, and magneto-optical properties of Co-doped CeO2-δ films,” J. Appl. Phys. 103(7), 07D138 (2008). [CrossRef]

16.

M. Bolduc, A. R. Taussig, A. Rajamani, G. F. Dionne, and C. A. Ross, “Magnetism and magneto optical effects in Ce-Fe Oxides,” IEEE. Trans. Mag. 42(10), 3093–3095 (2006). [CrossRef]

17.

D. C. Hutchings, “Prospects for the implementation of magneto-optic elements in optoelectronic integrated circuits: a personal perspective,” J. Phys. D. 36(18), 2222–2229 (2003). [CrossRef]

18.

T. Körner, A. Heinrich, M. Weckerle, P. Roocks, and B. Strizker, “Integration of magneto-optical active bismuth iron garnet on nongarnet substrates,” J. Appl. Phys. 103(7), 07B337 (2008). [CrossRef]

19.

J. Ostorero and M. Guillot, “Magneto-optical properties of Sc-substituted dysprosium iron garnet single crystals,” J. Appl. Phys. 91(10), 7296–7298 (2002). [CrossRef]

20.

M. Chandra Sekhar, J. Y. Hwang, M. Ferrera, Y. Linzon, L. Razzari, C. Harnagea, M. Zaezjev, A. Pignolet, and R. Morandotti, “Strong enhancement of the Faraday rotation in Ce and Bi comodified epitaxial iron garnet thin films,” Appl. Phys. Lett. 94(18), 181916 (2009). [CrossRef]

21.

J. Y. Hwang, R. Morandotti, and A. Pignolet, “Strong Faraday rotation in Ce and Bi comodified epitaxial iron garnet films: valence control through strain engineering,” Appl. Phys. Lett. 99(5), 051916 (2011). [CrossRef]

22.

B. M. Holmes and D. C. Hutchings, “Demonstration of quasi-phase-matched nonreciprocal polarization rotation in III-V semiconductor waveguides incorporating magneto-optic upper claddings,” Appl. Phys. Lett. 88(6), 061116 (2006). [CrossRef]

23.

Z. Yu and S. Fan, “Complete optical isolation created by indirect interband photonic transitions,” Nat. Photonics 3(2), 91–94 (2009). [CrossRef]

24.

L. Bi, J. Hu, P. Jiang, D. H. Kim, G. F. Dionne, L. C. Kimerling, and C. A. Ross, “On chip optical isolation in monolithically integrated non-reciprocal optical resonators,” Nat. Photonics 5(12), 758–762 (2011). [CrossRef]

25.

J. Fujita, M. Levy, R. M. Osgood Jr, L. Wilkens, and H. Dotsch, “Waveguide optical isolator based on Mach-Zehnder interferometer,” Appl. Phys. Lett. 76(16), 2158 (2000). [CrossRef]

26.

T. Mizumoto, K. Oochi, T. Harada, and Y. Naito, “Measurement of optical nonreciprocal phase shift in a Bi-substituted Gd3Fe5O12 film and application to waveguide-type optical circulator,” J. Lightwave Technol. 4(3), 347–352 (1986). [CrossRef]

27.

H. Dötsch, N. Bahlmann, O. Zhuromskyy, M. Hammer, L. Wilkens, R. Gerhardt, P. Hertel, and A. F. Popkov, “Application of magneto-optical waveguides in integrated optics,” J. Opt. Soc. Am. B 22, 240–253 (2005). [CrossRef]

28.

H. Y. Wong, W. K. Tan, A. C. Bryce, J. H. Marsh, J. M. Arnold, A. Krysa, and M. Sorel, “Current injection tunable monolithically integrated InGaAs-InAlGaAs asymmetric Mach-Zehnder interferometer using quantum well intermixing,” IEEE Photon. Technol. Lett. 17(8), 1677–1679 (2005). [CrossRef]

29.

H. Yokoi, T. Mizumoto, N. Shinjo, N. Futakuchi, and Y. Nakano, “Demonstration of an optical isolator, with a semiconductor guiding layer that was obtained by use of a nonreciprocal phase shift,” Appl. Opt. 39(33), 6158–6164 (2000). [CrossRef] [PubMed]

30.

Y. Shoji, T. Mizumoto, H. Yokoi, I. W. Hsieh, and R. M. Osgood Jr., “Magneto optical isolator with silicon waveguides fabricated by direct bonding,” Appl. Phys. Lett. 92(7), 071117 (2008). [CrossRef]

31.

D. B. Chrisey and G. K. Hubler, Pulsed Laser Deposition of thin films (Wiley Interscience, 1994).

32.

A. Ohtomo and A. Tsukazaki, “Pulsed laser deposition of thin films superlattices based on ZnO,” Semicond. Sci. Technol. 20(4), S1–S12 (2005). [CrossRef]

33.

R. Eason, Pulsed Laser Deposition of Thin Films: Applications-led Growth of Functional Materials, (John Wiley & Sons, Inc, 2007), Chap. 1.

34.

M. Chandrasekhar, “Structural and dielectric properties of Ba0.5Sr0.5TiO3 thin films grown on LAO with homo-epitaxial layer for tunable applications,” Int. J. Mod. Phys. B 18(15), 2153–2168 (2004). [CrossRef]

35.

M. Zaezjev, M. Chandrasekhar, M. Ferrera, L. Razzari, B. Holmes, M. Sorel, D. Hutchings, A. Pignolet, and R. Morandotti, “Crystallization of yttrium –iron garnet (YIG) in thin films: nucleation and growth aspect” in Proceedings of Materials and Hyperintegration Challenges in Next-Generation Interconnect technology, MRS proceedings (2007), 1036–M04–19.

36.

M. Zaezjev, M. Chandrasekhar, M. Ferrera, L. Razzari, A. Pignolet, R. Morandotti, B. Holmes, M. Sorel, and D. Hutchings, “Effect of the Foreign Phases on the crystallization and Growth of Magnetooptic garnet Films, in conference on Lasers and Electro-Optics/Quantum Electronics and Laser science Conference and Photonic Applications Systems Technologies, OSA technical digest (CD) (Optical Society of America, 2008) paper CThM5.

37.

W. K. Lee, H. Y. Wong, K. Y. Chan, T. K. Yong, S. S. Yap, and T. Y. Tou, “Effects of laser fluence on the structural properties of pulsed laser deposited ruthenium thin films” Appl. Phys. A. Mater. Sci. Process. 100(2), 561–568 (2010). [CrossRef]

38.

S. Kang, S. Yin, V. Adyam, Q. Li, and Y. Zhu, “Bi3Fe4Ga1O12 Garnet properties and its application to ultrafast switching in the visible spectrum,” IEEE Trans. Magn. 43(9), 3656–3660 (2007). [CrossRef]

39.

S. Geller and M. A. Gilleo, “The crystal structure and ferrimagnetism of yttrium–iron garnet Y3Fe2(FeO4)3,” J. Phys. Chem. Solids 3(1–2), 30–36 (1957). [CrossRef]

40.

M. O. Scully and M. S. Zubary, Quantum optics, (Cambridge University Press, 1997).

OCIS Codes
(160.3820) Materials : Magneto-optical materials
(230.2240) Optical devices : Faraday effect
(310.1860) Thin films : Deposition and fabrication

ToC Category:
Thin Films

History
Original Manuscript: February 8, 2012
Revised Manuscript: March 15, 2012
Manuscript Accepted: March 19, 2012
Published: April 12, 2012

Citation
M. Chandra Sekhar, Mahi R. Singh, Shantanu Basu, and Sai Pinnepalli, "Giant Faraday rotation in BixCe3-xFe5O12 epitaxial garnet films," Opt. Express 20, 9624-9639 (2012)
http://www.opticsinfobase.org/oe/abstract.cfm?URI=oe-20-9-9624


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References

  1. M. Levy, “The on-chip integration of magnetooptic waveguide isolators,” IEEE J. Sel. Top. Quantum Electron.8(6), 1300–1306 (2002). [CrossRef]
  2. A. K. Zvezdin and V. A. Kotov, Modern magneto-optics and magneto optical materials, (IOP publishing, Bristol, 1997).
  3. S. Kahl, S. I. Khartsev, A. M. Grishin, K. Kawano, G. Kong, R. A. Chakalov, and J. S. Abell, “Structure, microstructure, and magneto-optical properties of laser deposited Bi3Fe5O12/Gd3Ga5O12 (111) films,” J. Appl. Phys.91(12), 9556–9560 (2002). [CrossRef]
  4. Z. C. Xu, “Magnetooptic caracteristiques of BiTbGaIG film/TbYbBiIG bulk crystal composite structure in 1550 nm band,” Appl. Phys. Lett.89(3), 032501 (2006). [CrossRef]
  5. R. G. David, Fiber Optic Reference Guide, 3rd ed. (Boston Focal Press, 2002), p. 5.
  6. G. B. Scott and D. E. Lacklison, “Magnetooptic properties and applications of bismuth substituted iron garnets,” IEEE Trans. Magn.12(4), 292–311 (1976). [CrossRef]
  7. T. Okuda, N. Koshizuka, K. Hayashi, T. Takahashi, H. Kotani, and H. Yamamoto, “Epitaxial growth of Bi-substituted yttrium iron garnet films by ion beam sputtering,” Advances in magneto-optics, Proceedings. Int. Symp. Magneto-optics, J. Magn. Soc. Jpn. 11, Supplement S1, 179–182 (1987).
  8. B. Teggart, R. Atkinson, and I. W. Salter, “Enhancement of the polar Kerr effect in bismuth-substituted DyGa iron garnet thin films,” J. Phys. D Appl. Phys.31(19), 2442–2446 (1998). [CrossRef]
  9. M. Inoue, K. Arai, T. Fuji, and M. Abe, “One-dimensional magneto photonic crystals,” J. Appl. Phys.85(8), 5768–5770 (1999). [CrossRef]
  10. Y. H. Kim, J. S. Kim, S. I. Kim, and M. Levy, “Epitaxial growth and properties of Bi-substituted yttrium-iron garnet films grown on (111) gadolinium-gallium-garnet substrates by using rf magnetron sputtering,” J. Korean Phys. Soc.43(3), 400–405 (2003).
  11. S. I. Khartsev and A. M. Grishin, “[Bi3Fe5O12/Gd3Ga5O12] magneto-optical photonic crystals,” Appl. Phys. Lett.87(12), 122504 (2005). [CrossRef]
  12. R. Lux, A. Heinrich, S. Leitenmeier, T. Korner, M. Herbort, and B. Stritzker, “Pulsed-laser deposition and growth studies of Bi3Fe5O12 thin films,” J. Appl. Phys.100(11), 113511 (2006). [CrossRef]
  13. M. Vasiliev, K. E. Alameh, V. A. Kotov, and Y. T. Lee, “ Nanostructured engineered materials with high magneto-optic performance for integrated photonics applications,” in Proceedings. IEEE Photonics Global @Singapore, (IPGC 2008).
  14. T. Shintaku, A. Tate, and S. Mino, “Ce-substituted yttrium iron garnet films prepared on Gd3Sc2Ga3O12 garnet substrates by sputter epitaxy,” Appl. Phys. Lett.71(12), 1640–1642 (1997). [CrossRef]
  15. L. Bi, H. S. Kim, G. F. Dionne, S. A. Speakman, D. Bono, and C. A. Ross, “Structural, magnetic, and magneto-optical properties of Co-doped CeO2-δ films,” J. Appl. Phys.103(7), 07D138 (2008). [CrossRef]
  16. M. Bolduc, A. R. Taussig, A. Rajamani, G. F. Dionne, and C. A. Ross, “Magnetism and magneto optical effects in Ce-Fe Oxides,” IEEE. Trans. Mag.42(10), 3093–3095 (2006). [CrossRef]
  17. D. C. Hutchings, “Prospects for the implementation of magneto-optic elements in optoelectronic integrated circuits: a personal perspective,” J. Phys. D.36(18), 2222–2229 (2003). [CrossRef]
  18. T. Körner, A. Heinrich, M. Weckerle, P. Roocks, and B. Strizker, “Integration of magneto-optical active bismuth iron garnet on nongarnet substrates,” J. Appl. Phys.103(7), 07B337 (2008). [CrossRef]
  19. J. Ostorero and M. Guillot, “Magneto-optical properties of Sc-substituted dysprosium iron garnet single crystals,” J. Appl. Phys.91(10), 7296–7298 (2002). [CrossRef]
  20. M. Chandra Sekhar, J. Y. Hwang, M. Ferrera, Y. Linzon, L. Razzari, C. Harnagea, M. Zaezjev, A. Pignolet, and R. Morandotti, “Strong enhancement of the Faraday rotation in Ce and Bi comodified epitaxial iron garnet thin films,” Appl. Phys. Lett.94(18), 181916 (2009). [CrossRef]
  21. J. Y. Hwang, R. Morandotti, and A. Pignolet, “Strong Faraday rotation in Ce and Bi comodified epitaxial iron garnet films: valence control through strain engineering,” Appl. Phys. Lett.99(5), 051916 (2011). [CrossRef]
  22. B. M. Holmes and D. C. Hutchings, “Demonstration of quasi-phase-matched nonreciprocal polarization rotation in III-V semiconductor waveguides incorporating magneto-optic upper claddings,” Appl. Phys. Lett.88(6), 061116 (2006). [CrossRef]
  23. Z. Yu and S. Fan, “Complete optical isolation created by indirect interband photonic transitions,” Nat. Photonics3(2), 91–94 (2009). [CrossRef]
  24. L. Bi, J. Hu, P. Jiang, D. H. Kim, G. F. Dionne, L. C. Kimerling, and C. A. Ross, “On chip optical isolation in monolithically integrated non-reciprocal optical resonators,” Nat. Photonics5(12), 758–762 (2011). [CrossRef]
  25. J. Fujita, M. Levy, R. M. Osgood, L. Wilkens, and H. Dotsch, “Waveguide optical isolator based on Mach-Zehnder interferometer,” Appl. Phys. Lett.76(16), 2158 (2000). [CrossRef]
  26. T. Mizumoto, K. Oochi, T. Harada, and Y. Naito, “Measurement of optical nonreciprocal phase shift in a Bi-substituted Gd3Fe5O12 film and application to waveguide-type optical circulator,” J. Lightwave Technol.4(3), 347–352 (1986). [CrossRef]
  27. H. Dötsch, N. Bahlmann, O. Zhuromskyy, M. Hammer, L. Wilkens, R. Gerhardt, P. Hertel, and A. F. Popkov, “Application of magneto-optical waveguides in integrated optics,” J. Opt. Soc. Am. B22, 240–253 (2005). [CrossRef]
  28. H. Y. Wong, W. K. Tan, A. C. Bryce, J. H. Marsh, J. M. Arnold, A. Krysa, and M. Sorel, “Current injection tunable monolithically integrated InGaAs-InAlGaAs asymmetric Mach-Zehnder interferometer using quantum well intermixing,” IEEE Photon. Technol. Lett.17(8), 1677–1679 (2005). [CrossRef]
  29. H. Yokoi, T. Mizumoto, N. Shinjo, N. Futakuchi, and Y. Nakano, “Demonstration of an optical isolator, with a semiconductor guiding layer that was obtained by use of a nonreciprocal phase shift,” Appl. Opt.39(33), 6158–6164 (2000). [CrossRef] [PubMed]
  30. Y. Shoji, T. Mizumoto, H. Yokoi, I. W. Hsieh, and R. M. Osgood., “Magneto optical isolator with silicon waveguides fabricated by direct bonding,” Appl. Phys. Lett.92(7), 071117 (2008). [CrossRef]
  31. D. B. Chrisey and G. K. Hubler, Pulsed Laser Deposition of thin films (Wiley Interscience, 1994).
  32. A. Ohtomo and A. Tsukazaki, “Pulsed laser deposition of thin films superlattices based on ZnO,” Semicond. Sci. Technol.20(4), S1–S12 (2005). [CrossRef]
  33. R. Eason, Pulsed Laser Deposition of Thin Films: Applications-led Growth of Functional Materials, (John Wiley & Sons, Inc, 2007), Chap. 1.
  34. M. Chandrasekhar, “Structural and dielectric properties of Ba0.5Sr0.5TiO3 thin films grown on LAO with homo-epitaxial layer for tunable applications,” Int. J. Mod. Phys. B18(15), 2153–2168 (2004). [CrossRef]
  35. M. Zaezjev, M. Chandrasekhar, M. Ferrera, L. Razzari, B. Holmes, M. Sorel, D. Hutchings, A. Pignolet, and R. Morandotti, “Crystallization of yttrium –iron garnet (YIG) in thin films: nucleation and growth aspect” in Proceedings of Materials and Hyperintegration Challenges in Next-Generation Interconnect technology, MRS proceedings (2007), 1036–M04–19.
  36. M. Zaezjev, M. Chandrasekhar, M. Ferrera, L. Razzari, A. Pignolet, R. Morandotti, B. Holmes, M. Sorel, and D. Hutchings, “Effect of the Foreign Phases on the crystallization and Growth of Magnetooptic garnet Films, in conference on Lasers and Electro-Optics/Quantum Electronics and Laser science Conference and Photonic Applications Systems Technologies, OSA technical digest (CD) (Optical Society of America, 2008) paper CThM5.
  37. W. K. Lee, H. Y. Wong, K. Y. Chan, T. K. Yong, S. S. Yap, and T. Y. Tou, “Effects of laser fluence on the structural properties of pulsed laser deposited ruthenium thin films” Appl. Phys. A. Mater. Sci. Process.100(2), 561–568 (2010). [CrossRef]
  38. S. Kang, S. Yin, V. Adyam, Q. Li, and Y. Zhu, “Bi3Fe4Ga1O12 Garnet properties and its application to ultrafast switching in the visible spectrum,” IEEE Trans. Magn.43(9), 3656–3660 (2007). [CrossRef]
  39. S. Geller and M. A. Gilleo, “The crystal structure and ferrimagnetism of yttrium–iron garnet Y3Fe2(FeO4)3,” J. Phys. Chem. Solids3(1–2), 30–36 (1957). [CrossRef]
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