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Physical Properties and Behaviour of Highly Bi-Substituted Magneto-Optic Garnets for Applications in Integrated Optics and Photonics

Physical Properties and Behaviour of Highly Bi-Substituted Magneto-Optic Garnets for Applications... Hindawi Publishing Corporation Advances in Optical Technologies Volume 2011, Article ID 971267, 7 pages doi:10.1155/2011/971267 Research Article Physical Properties and Behaviour of Highly Bi-Substituted Magneto-Optic Garnets for Applications in Integrated Optics and Photonics 1 1 1, 2 3 Mohammad Nur-E-Alam, Mikhail Vasiliev, Kamal Alameh, and Viacheslav Kotov Electron Science Research Institute, Edith Cowan University, Joondalup, WA 6027, Australia Department of Nanobio Materials and Electronics, GIST, Gwangju, Republic of Korea Institute of Radio Engineering and Electronics, Russian Academy of Sciences, 11 Mohovaya St., Moscow 125009, Russia Correspondence should be addressed to Mohammad Nur-E-Alam, m.nur-e-alam@ecu.edu.au and Mikhail Vasiliev, m.vasiliev@ecu.edu.au Received 31 March 2011; Accepted 10 June 2011 Academic Editor: Steve Blair Copyright © 2011 Mohammad Nur-E-Alam et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. Rare-earth and Bi-substituted iron garnet thin film materials exhibit strong potential for application in various fields of science and frontier optical technologies. Bi-substituted iron garnets possess extraordinary optical and MO properties and are still considered as the best MO functional materials for various emerging integrated optics and photonics applications. However, these MO garnet materials are rarely seen in practical photonics use due to their high optical losses in the visible spectral region. In this paper, we report on the physical properties and magneto-optic behaviour of high-performance RF sputtered highly bismuth-substituted iron garnet and garnet-oxide nanocomposite films of generic composition type (Bi, Dy/Lu) (Fe, Ga/Al) O . Our newly synthesized 3 5 12 garnet materials form high-quality nanocrystalline thin film layers which demonstrate excellent optical and MO properties suitable for a wide range of applications in integrated optics and photonics. 1. Introduction of applying external magnetic fields on a nanosecond time scale. Highly bismuth-substituted iron garnets are becoming It is now more than 40 years since the giant magneto-optical more and more attractive nowadays for various application effects in bismuth-substituted iron garnets (Bi:IG) were fields ranging from magnetic data recovery to quantum op- reported first in 1969 and used extensively for fabricating tical information processing [10–19]. Extensive studies have various magnetic recording media. But the synthesis efforts been conducted by multiple groups working world-wide to aimed at controlling the properties of Bi:IG compounds con- synthesize new garnet materials with properties suitable for taining various metal dopants have started back in 1960s, and various emerging technologies and having a high Bi content different methods were used, including Pulsed Laser Depo- and also other metal-atom dopants like Ga or Al within the sition (PLD), Liquid Phase Epitaxy (LPE), Ion Beam Sput- garnet structure. The physical properties (optical, magnetic, tering (IBS), Reactive Ion Beam Sputtering (RIBS), Sol-gel and MO) of all garnet materials depend significantly not only process, and RF magnetron sputtering [1–9]. Bi:IGs are still on the Bi content and the substitution of other extra atoms considered to be the best magneto-optic (MO) material and dopants within the sublattices of the garnet structure, type among all known semitransparent materials and are but also on the multiple process parameters relevant to the therefore of interest for various optical, MO, and other synthesis of Bi:IGs [3]. The synthesis of high-quality Bi:IG applications. The extraordinary MO properties of highly Bi- thin film materials is usually a very complex and multi- substituted iron garnet materials allow the modulation of the step process sequence which also requires complex multipa- polarisation state and intensity of polarized light by means rameter process optimizations applied at both the deposition 2 Advances in Optical Technologies and annealing stages. RF magnetron sputtering using low- 2.2. Oven Annealing Heat Treatment. The as-deposited films pressure (1–5 mTorr) argon (Ar) plasma is one of the most (amorphous-phase layers) were placed into a conventional flexible approaches to deposit MO garnet materials. The abil- box-furnace-type oven annealing system to anneal them ity to vary the substrate temperature during the deposition in air atmosphere using the appropriate composition-de- and also the possibility of growing the films on relatively cold pendent optimized isothermal crystallization regimes. The substrates are very important for the integration of Bi:IG annealing processes were run to crystallize the sputtered thin films into optical devices. We prepare highly Bi-substituted films inside the oven with temperature ramp rates (up and dysprosium (or lutetium) iron garnet thin films using RF down) in between 3–5 C/min, for a number of different sputtering followed by the conventional (postdeposition) annealing durations. We used low rates of temperature ramp- oven annealing in air atmosphere. Our MO garnet thin film ing during the annealing processes for our garnet-oxide materials are highly competitive (in terms of MO figure of composite materials to avoid the film surface degradation merit) with all other garnet materials synthesized to date by and microcrack formation in samples. We found that the using various modern microfabrication technologies. optimization of annealing regimes (both temperature and In this paper, we report on the physical properties and annealing process durations were optimized) for our highly behaviour (especially the magnetic switching behaviour) Bi-substituted garnet materials was strongly dependent on of several RF-sputtered high-performance, highly bismuth- the composition of films. Figure 2 shows a photograph of substituted ferrimagnetic garnet materials which are suitable (150 W Bi Dy Fe Ga O +30W Bi O , or having 2 1 4.3 0.7 12 2 3 for integration into various photonic devices and for many 37 vol.% of excess Bi O ) composite films on Corning 1737 2 3 magneto-optic applications. glass (larger sample) and on a GGG (smaller sample) sub- strate having hazy and optically damaged (scatterer-type) 2. Experimental surfaces due to over-annealing. These films were annealed in air atmosphere for only 30 minutes at 520 C, with 2.1. RF Sputtering Processes and Thin Film Growth. Highly a temperature ramp (up/down) rate of 5 C/min. However, bismuth-substituted garnet films and also various cosput- this amount of thermal exposure was already excessive, due tered nanocomposite garnet-bismuth oxide thin films were to the rather high bismuth content of the deposited layers. fabricated by using RF magnetron sputtering system (Korea It is evident that either the annealing temperature or the Vacuum Technology Ltd KVS-T 4065). The garnet and annealing duration or both were not optimized to form opti- composite garnet-oxide thin films of different thicknesses cally flat nanocrystalline layers from the amorphous phase of (up to 1500 nm) were prepared in a high-vacuum chamber these garnet-oxide composites. So it is one of the important using low-pressure argon (Ar) plasma at different sub- factors of garnet thin films synthesis to find an optimized strate temperatures ranging between 250–680 C during the annealing regimes as the optical and MO properties are deposition. We prepared several batches of garnet thin vitally related to the optimization of the annealing regimes. films and also garnet-bismuth oxide composite films having Even though these films were optically spoiled, they still did different volumetric contents of Bi O added by cosputtering 2 3 demonstrate some useful MO properties in terms of Faraday from a separate target. The nominal stoichiometries of the rotation per unit film thickness as reported in a previous sputtering targets Bi Dy Fe Ga O (where m = 2and m 3−m 5−n n 12 publication [10]. n = 1 and 0.7) and Bi Lu Fe Al O (where a = 1.2 a 3−a 5−b b 12 and b = 1.4) based on high-purity (99.99%) oxide material 2.3. Thin-Film Materials Characterization. The structural, mixes were selected to experiment with different levels optical, magnetic, and MO properties of high-quality an- of magnetostriction-induced uniaxial magnetic anisotropy. nealed garnet thin films were subjected to characterization A separate Bi O target was used as an external source 2 3 using a number of characterization techniques. The crystal of Bi oxide (and also Bi) content for incorporation into structure and impurity phases of garnet and garnet-bismuth the nanocomposite materials during cosputtering processes. oxide thin films of type (BiDy) (Fe,Ga) O have been ana- A schematic diagram of our cosputtering geometry is shown 5 lyzed using X-ray diffractometry (XRD) data generated by in Figure 1 (up to two guns were used concurrently in Panalytical XPert Pro X-ray diffractometer configured for our experiments). The target materials (garnet and oxide) near-grazing-incidence powder diffraction measurements of 3 diameter were placed at three RF guns of the using the CuK (λ = 0.15406 nm) radiation. The optical down-sputtering system having about 18 cm of source- α1 properties of garnet films were investigated by variable- to-substrate separation. All the guns with independently angle spectroscopic ellipsometry and also by deriving the activated shutters are placed at the corners of the equilateral absorption coefficient spectra, while the measurements of triangle and tilted towards the substrates. The substrates’ Faraday rotation hysteresis loops revealed the most impor- stage rotation was adjusted to be near 40–50 rpm during tant magnetic and MO properties of the garnet films. The the deposition processes to provide a good deposition thickness/composition uniformity of sputtered films on all specific Faraday rotation measurements were performed al- most across the entire visible spectral region by using substrates. The film thicknesses were always measured in two ways; thicknesses were monitored during the deposition and several laser light sources, a Thorlabs PAX polarimeter and also remeasured after deposition using the spectrally best- an electromagnet. A transmission-mode polarizing micro- fitted transmission spectra and also their measured refractive scope (Leitz Orthoplan) was used to observe the magnetic index and absorption spectra. domain patterns of garnet films. Gun3 (Bi, Lu) (Fe, Al) O 5 12 Advances in Optical Technologies 3 Gun 2 RF power Bi O 2 3 Bi O (Bi, Dy, Lu) (Fe, Ga, Al) O 2 3 3 5 12 Ar plasma (BiLu) (FeAL) O :Bi O 3 5 12 2 3 film (amorphous) Amorphous 6R Amorphous film 4R 8R 10R (BiDy) (FeGa) O :Bi O 3 5 12 2 3 Heat treatment film (annealed) Crystal Crystallized film Substrate (a) (b) Figure 1: (a) Schematic diagram of the cosputtering system geometry, (b) flow chart of garnet-bismuth oxide cosputtered thin films processing. We have previously not only reported on the optical and magneto-optical properties of the sputtered (Bi, Dy) (Fe, Ga) O material type and its nanocomposite 5 12 derivativesoftype(Bi,Dy) (Fe, Ga) O :Bi O but also doc- 12 2 3 3 5 umented their annealing behaviour and the effects of thermal exposure on the resulting optical and MO properties [10, 16]. We have also reported on the synthesis of RF-sputtered garnet materials of composition type Bi Lu Fe Al O 1.8 1.2 3.6 1.4 12 Figure 2: Photographs of a correctly annealed garnet-oxide com- for the first time, and we believe that no physical vapour posite thin film and two over-annealed films of composition type deposition methods have so far been used previously to Bi Dy Fe Ga O :Bi O sputtered onto Corning 1737 (larger 2 1 4.3 0.7 12 2 3 synthesize this material type with a high Bi-content (near samples) and GGG (smaller sample) substrates. The transparent two formula units) [17]. The codeposited nanocomposite film (on the left) has a smaller thickness and high surface quality. derivatives of type (Bi, Lu) (Fe, Al) O :Bi O have been 12 2 3 The two over-annealed films were oven treated at 520 C for 30 min. 3 5 under investigation, and the detailed results will be reported elsewhere soon. The addition of excess Bi O to the base 2 3 garnet composition of type Bi Lu Fe Al O during 1.8 1.2 3.6 1.4 12 cosputtering did not have much influence on the Faraday 3. Results and Discussion rotation of the garnet layers but significantly reduced the The correctly annealed highly Bi-substituted magneto-optic optical absorption. The garnet-oxide composite films of type doped-iron-garnet thin films demonstrated excellent optical (Bi, Lu) (Fe, Al) O :Bi O (4.5 vol.% extra bismuth oxide) 3 5 12 2 3 properties across the visible and near-infrared spectral range. possessed extremely large MO figure of merit (more than 50 We observed very similar behaviours of the optical absorp- at 635 nm), which was more than three times higher than tion spectra in both types of our sputtered garnet films that of the typical garnet layer (Figure 4). Figure 4. shows (dysprosium iron garnets and lutetium iron garnets). It is the values of the specific Faraday rotation achieved and MO important to note that lower absorption coefficients were figures of merit measured using 532 nm and 635 nm light. always observed (as was expected) in the cosputtered garnet- The X-ray diffraction patterns of Bi Dy Fe Ga O and 2 1 4 1 12 bismuth oxide composite thin films compared to the absorp- (BiDy) (FeGa) O :Bi O layers synthesized on glass sub- 12 2 3 tion of typical (stoichiometrically deposited) garnet layers. strates are presented in Figure 5. The data reveals the nano- Figure 3 shows the absorption coefficient spectra measured crystalline microstructure of the annealed garnet materials in typical (Bi, Dy, Lu) (Fe, Ga, Al) O garnet layers and also and the body-centered cubic lattice structure type, as well as 5 12 those measured in the best-performing cosputtered garnet- only one identifiable impurity phase (Fe O ) being present. 3 4 oxide (Bi, Dy, Lu) (Fe, Ga, Al) O :Bi O composite layers The addition of extra Bi O always reduced the relative inten- 12 2 3 2 3 sputtered onto GGG (111) substrates. Similar trends in the sities of the iron-oxide diffraction peaks, as witnessed by the absorption coefficient spectra were also observed in the films diffraction datasets of the films synthesized by cosputtering. sputtered onto the glass (Corning 1737) substrates. This indicates the presence of less iron oxide outside Gun 1 (Bi, Dy) (Fe, Ga) O 5 12 4 Advances in Optical Technologies 500 550 600 650 Wavelength (nm) Typical Bi Dy Fe Ga O garnet film on GGG, annealed for 1 hr at 680 C 2 1 4.3 0.7 12 Typical Bi Dy Fe Ga O garnet film on GGG, annealed for 1 hr at 700 C 2 1 4 1 12 Typical Bi Lu Fe Al O garnet film on GGG, annealed for 1 hr at 650 C 1.8 1.2 3.6 1.4 12 Bi Dy Fe Ga O :Bi O (est. 23.6 vol%) composite on GGG, annealed for 1 hr at 560 C 2 1 4.3 0.7 12 2 3 Bi Dy Fe Ga O :Bi O (est. 23.3 vol%) composite on GGG, annealed for 2 hrs at 580 C 2 1 4 1 12 2 3 Bi Lu Fe Al O :Bi O (est. 4.5 vol%) composite on GGG, annealed for 10 hrs at 610 C 1.8 1.2 3.6 1.4 12 2 3 Figure 3: Derivedabsorptioncoefficient spectra of the best-performing garnet layer types and these of the garnet-oxide composite (having different vol.% content of excess Bi O ) films deposited onto GGG (111) substrates. 2 3 50 10 40 8 30 6 20 4 10 2 0 0 Composite type 532 nm MO figure of merit 635 nm MO figure of merit Faraday rotation at 532 nm Faradayrotationat635nm Figure 4: Summary of the measured specific Faraday rotation data (dashed lines) and MO figures of merit (bar diagrams) of different garnet and garnet-oxide composite layer types; the highest values (of the specific Faraday rotation and MO figure of merit) achieved in our experiments so far are indicated. the garnet nanocrystallites. No diffraction peaks character- The effects of extra bismuth oxide incorporation on the istic of Bi O have been observed since the bismuth oxide MO properties were investigated, and also the influence 2 3 remained in its amorphous phase even after the annealing of the volumetric content of extra bismuth oxide was ob- treatments. served (Figure 6(a)). Our experimental results revealed Figure 6 shows the hysteresis loops of specific Faraday that by controlling the volumetric content of extra Bi O 2 3 rotation at 532 nm measured in several best-performing gar- it was possible to control (to some degree) the magnetic net-bismuth oxide nanocomposite films, which had different switching behaviour and the coercive force value of garnet- coercive force, saturation field, and switching field values. oxide nanocomposite media. This type of control over the −1 Absorption coefficient (cm ) MO figure of merit (degs) (BiDy) Fe Ga O 3 4 1 12 1.9 9.5 garnet 14.5 24.2 (BiDy) Fe Ga O + 3 4 1 12 23.3 vol% Bi O 2.6 2 3 9.8 25.7 composite 42.5 (BiDy) Fe Ga O 3 4.3 0.7 12 1.1 garnet 7.9 11.4 (BiDy) Fe Ga O + 3 4.3 0.7 12 1.6 23.6 vol% Bi O 2 3 10.1 29.2 composite 22.1 (BiLu) (FeAl) O 3 5 12 1.6 5.8 garnet 13.9 15.7 (BiLu) (FeAl) O + 3 5 12 6.1 1.7 4.5 vol% Bi O 2 3 22.1 composite 50.2 Specific Faraday rotation (deg/µm) Advances in Optical Technologies 5 (420) (422) Fe O 3 4 (642) Bi Dy Fe Ga O :Bi O composite film on glass, annealed at 580 C 2 1 4 1 12 2 3 (211) (400) (640) Fe O 3 4 (842) (444) (800) 600 (220) Bi Dy Fe Ga O :Bi O composite film on glass, annealed at 560 C 2 1 4.3 0.7 12 2 3 (321) Fe O 3 4 (521) Bi Dy Fe Ga O film on galss, annealed at 620 C 2 1 4 1 12 10 20 30 40 50 60 70 80 2Θ (degs) Figure 5: X-ray diffraction patterns of several sputtered Bi-substituted thin-film garnet materials deposited onto glass substrates. 6 4 −1500 −1000 −500 500 1000 1500 −2500 −1500 −500 500 1500 2500 −1 6 Hc = (45 ± 5) Oe −2 5 and Hsat = 350 Oe −2 Hc Hc == (30 (30 ±± 5 5)) O Oee and and H Hsat sat == 270 270 O Oee 2 −4 −3 −400 −300 −200 −100 100 200 300 400 −4 −1 −6 −2 −3 −5 −4 −5 −8 −6 −6 Magnetic field (Oe) −7 −10 Magnetic field (Oe) Magnetic field (Oe) Typical Bi Lu Fe Al O garnet film Bi Dy Fe Ga O :Bi O composite 1.8 1.2 3.6 1.4 12 2 1 4 1 12 2 3 on GGG; Hc = (45 ± 5) Oe (about 22 vol% excess oxide) on GGG Composite Bi Lu Fe Al O :Bi O 1.8 1.2 3.6 1.4 12 2 3 Bi Dy Fe Ga O :Bi O composite 2 1 4 1 12 2 3 (4.5 vol%) film on GGG; Hc = (30 ± 5) Oe (about 20 vol% excess oxide) on GGG (a) (b) Figure 6: Hysteresis loops of specific Faraday rotation measured using a 532 nm laser source in several highly Bi-substituted iron garnet- bismuth oxide nanocomposite films of types (a) (BiDy) (FeGa) O :Bi O and (b) (BiLu) (FeAl) O :Bi O , deposited onto GGG (111) 5 12 2 3 3 5 12 2 3 substrates. magnetic properties can lead towards achieving tunability in [13]. On the other hand, rather low coercive force values magneto-photonic crystals, which is very essential for dif- were measured in the second type of thin film materials ferent types of applications including the optical isolators studied (bismuth-substituted lutetium iron garnets doped and optical polarization controllers. The experimental setup with aluminium) sputtered onto GGG (111) substrates. The for characterization of magneto-optic switching response measured coercive force for the films on GGG substrates as well as magnetization dynamics has been described in was about 45 Oe, whereas the addition of extra bismuth [20]. Nanosecond-range switching response times of below oxide into the films reduced the coercivity of the films 20 ns were measured previously in 1∼2 μm thick highly as indicated in the inset (Figure 6(b)). We measured a Bi-substituted iron garnet films of composition type high Faraday-effect magnetic field sensitivity within the (Bi, Dy) (Fe, Ga) O . Note that the high-speed switch- linear range of magnetizations of up to 42.8 /(cm·Oe) at 5 12 ing time constant of 2.4 ns has also been measured in 635 nm, which was higher than that obtained previously Bi Fe Ga O garnet films of 1 mm aperture size at 532 nm in epitaxial (BiLu) (FeGa) O films prepared by LPE [18]. 3 4 1 12 12 3 5 Specific Faraday rotation (deg/micron) Intensity (a.u.) Faraday rotation (deg/µm) MO ultrafast switches Garnet waveguides development Magnetic field sensors 6 Advances in Optical Technologies 20 µm 20 µm (a) (b) Figure 7: Magnetic domain patterns obtained in two different garnet-bismuth oxide composite thin films (a) Bi Dy Fe Ga O :Bi O , with 2 1 4 1 12 2 3 an est. 23% of excess oxide, and (b) Bi Lu Fe Al O :Bi O , with an est. 4.5% of excess bismuth oxide sputtered onto GGG (111) 1.8 1.2 3.6 1.4 12 2 3 substrates. and possess a significant in-plane magnetization component which will be especially suitable for the development of gar- net waveguides, nonreciprocal integrated optics components as well as the magnetic field imaging and sensing devices. 4. Applications of RF-Sputtered Garnet Materials MO garnet MO spatial light MO imaging Modern civilization demands superior technologies and materials modulators devices high-speed communication systems for achieving a better lifestyle. It is the challenge for modern science and tech- nology to serve the requirements of society by providing all required technological facilities through new research, inven- tions, and reconfiguration of the existing devices and tech- nologies. Materials science is one of the branches of science that can achieve rapid progress in research and applications for many new and existing technologies. A wide and growing range of applications require the design and development Figure 8: The existing and potential new application areas of MO of new photonic materials (including MO garnet materials) garnet materials. which can enable control over the interaction of light with matter. MO garnet materials, especially the Bi-substituted iron garnet compounds are very suitable for various applica- We also measured even lower coercive force values of less tions (Figure 8) including lightwave polarization controllers, than 20 Oe in thin films sputtered onto GGG at high MO flaw detection, high-density magnetic recording and substratetemperaturesnear680 C. MO data recovery, high-speed spatial and temporal light The magnetic domain structures observed in our two modulators, magnetic nanostructures for ultracold atoms different types of garnet-bismuth oxide composite thin films trapping, and the development of magnetic photonic crystals in the absence of externally applied magnetic fields are (MPCs). The combination of the remarkable properties of shown in Figure 7. The domain patterns were observed using magnetic garnet materials shows great promise for applica- a transmission-mode polarizing microscope. tions in next-generation integrated optics, nanophotonics, The combination of physical properties of the highly and also in reconfigurable photonics. The development of Bi-substituted iron garnets of both types shows a great new garnet-type materials by synthesizing Bi-substituted promise for the future development of different emerging iron garnets and their codeposited nanocomposite garnet- types of integrated and reconfigurable nanophotonic devices. oxide derivatives will not only allow the integration of Garnet thin films of type (BiDy) (FeGa) O demonstrated garnet-based components into existing integrated-optics 3 5 simultaneously a record high MO quality, and strong uni- manufacturing processes, but will also help achieve cost axial magnetic anisotropy will be attractive for visible-range efficiency by providing the functional materials which are and near-infrared applications, including the development technologically compatible with the presently used material of high-performance magnetic field visualizers and inte- combinations. That will have influence on numerous com- grated optical polarization controllers. The garnet films of munities, because most of the innovative technologies using type (BiLu) (FeAl) O feature magnetically soft behaviour these advanced materials will be easy to implement and less 3 5 Nonreciprocal devices MO circulator anddeflectors Magnetic component of MPCs Advances in Optical Technologies 7 costly. [8] Y. Zhang, X. Wang, H. Xia et al., “Characterization of Bi- substituted dysprosium iron garnet films prepared Sol-gel process,” Journal of Materials Sciences and Technology, vol. 20, no. 1, pp. 66–68, 2004. 5. Conclusions [9] M. Vasiliev, M. Nur-E-Alam, V. A. Kotov et al., “RF magnetron sputtered (BiDy) (FeGa) O :Bi O composite garnet-oxide We have synthesized a range of bismuth-substituted iron gar- 3 5 12 2 3 materials possessing record magneto-optic quality in the visi- net thin-film materials having different bismuth substitution ble spectral region,” Optics Express, vol. 17, no. 22, pp. 19519– levels and metal dopants using the RF magnetron sputtering 19535, 2009. technique, which is one of the most common physical vapour [10] M. Nur-E-Alam, M. Vasiliev, and K. Alameh, “Nano-struc- deposition methods. We have characterized the nanocrys- tured magnetic photonic crystals for magneto-optic polar- talline thin-film garnet materials crystallized using high-tem- ization controllers at the communication-band wavelengths,” perature oven processing and found the ways of achieving Optical and Quantum Electronics, vol. 41, no. 9, pp. 661–669, low optical absorption losses, relatively high specific Faraday rotation, and also some control over the magnetic switching [11] A. Abdelrahman, M. Vasiliev, K. Alameh, and P. Hannaford, behaviour. Our newly synthesized MO materials of two dif- “Asymmetrical two-dimensional magnetic lattices for ultra- ferent composition types possess record high MO figures of cold atoms,” Physical Review A, vol. 82, no. 1, Article ID 012320, 6 pages, 2010. merit in conjunction with other excellent physical properties [12] I. L. Lyubchanskii, N. N. Dadoenkova, M. I. Lyubchanskii, E. which are attractive for use in various integrated-optics and A. Shapovalov, and T. Rasing, “Magnetic photonic crystals,” photonics applications. Journal of Physics D, vol. 36, no. 18, pp. R277–R287, 2003. [13] S. Kang, S. Yin, V. Adyam, Q. Li, and Y. Zhu, “Bi Fe Ga O 3 4 1 12 garnet properties and its application to ultrafast switching in Acknowledgments the visible spectrum,” IEEE Transactions on Magnetics, vol. 43, no. 9, pp. 3656–3660, 2007. The authors would like to acknowledge the support of the [14] T. Kim, S. Nasu, and M. Shima, “Growth and magnetic behav- Faculty of Computing, Health and Science, Edith Cowan ior of bismuth substituted yttrium iron garnet nanoparticles,” University, Australia, and the Department of Nanobio Mate- Journal of Nanoparticle Research, vol. 9, no. 5, pp. 737–743, rials and Electronics, Gwangju Institute of Science and Tech- nology, Republic of Korea. They would also like to pay special [15] M. Vasiliev, M. Nur-E-Alam, K. Alameh et al., “Annealing thanks to the Materials Characterization Lab, Korea Optical behaviour and crystal structure of RF-sputtered Bi-substituted Technology Institute (KOPTI, Gwangju, South Korea) for dysprosium iron-garnet films having excess co-sputtered Bi- performing the XRD data acquisition. oxide content,” Journal of Physics D, vol. 44 , article 075002, no. 7, 2011. [16] M. Nur-E-Alam, M. Vasiliev, K. Alameh, and V. Kotov, “High-quality RF-sputtered magneto-optic garnet films of References Bi Lu Fe Al O with low coercivity for applications in 1.8 1.2 3.6 1.4 12 [1] C. F. Buhrer, “Faraday rotation and dichroism of bismuth cal- integrated optics, imaging and sensing devices,” in Proceed- cium vanadium iron garnet,” Journal of Applied Physics, vol. ings of the International Conference on High-capacity Optical 40, no. 11, pp. 4500–4502, 1969. Networks and Enabling Technologies Conference,Cairo,Egypt, December 2010. [2] G.B.Scott andD.E.Lacklison,“Magnetooptic properties [17] N. 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Physical Properties and Behaviour of Highly Bi-Substituted Magneto-Optic Garnets for Applications in Integrated Optics and Photonics

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Hindawi Publishing Corporation
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Copyright © 2011 Mohammad Nur-E-Alam et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
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10.1155/2011/971267
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Hindawi Publishing Corporation Advances in Optical Technologies Volume 2011, Article ID 971267, 7 pages doi:10.1155/2011/971267 Research Article Physical Properties and Behaviour of Highly Bi-Substituted Magneto-Optic Garnets for Applications in Integrated Optics and Photonics 1 1 1, 2 3 Mohammad Nur-E-Alam, Mikhail Vasiliev, Kamal Alameh, and Viacheslav Kotov Electron Science Research Institute, Edith Cowan University, Joondalup, WA 6027, Australia Department of Nanobio Materials and Electronics, GIST, Gwangju, Republic of Korea Institute of Radio Engineering and Electronics, Russian Academy of Sciences, 11 Mohovaya St., Moscow 125009, Russia Correspondence should be addressed to Mohammad Nur-E-Alam, m.nur-e-alam@ecu.edu.au and Mikhail Vasiliev, m.vasiliev@ecu.edu.au Received 31 March 2011; Accepted 10 June 2011 Academic Editor: Steve Blair Copyright © 2011 Mohammad Nur-E-Alam et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. Rare-earth and Bi-substituted iron garnet thin film materials exhibit strong potential for application in various fields of science and frontier optical technologies. Bi-substituted iron garnets possess extraordinary optical and MO properties and are still considered as the best MO functional materials for various emerging integrated optics and photonics applications. However, these MO garnet materials are rarely seen in practical photonics use due to their high optical losses in the visible spectral region. In this paper, we report on the physical properties and magneto-optic behaviour of high-performance RF sputtered highly bismuth-substituted iron garnet and garnet-oxide nanocomposite films of generic composition type (Bi, Dy/Lu) (Fe, Ga/Al) O . Our newly synthesized 3 5 12 garnet materials form high-quality nanocrystalline thin film layers which demonstrate excellent optical and MO properties suitable for a wide range of applications in integrated optics and photonics. 1. Introduction of applying external magnetic fields on a nanosecond time scale. Highly bismuth-substituted iron garnets are becoming It is now more than 40 years since the giant magneto-optical more and more attractive nowadays for various application effects in bismuth-substituted iron garnets (Bi:IG) were fields ranging from magnetic data recovery to quantum op- reported first in 1969 and used extensively for fabricating tical information processing [10–19]. Extensive studies have various magnetic recording media. But the synthesis efforts been conducted by multiple groups working world-wide to aimed at controlling the properties of Bi:IG compounds con- synthesize new garnet materials with properties suitable for taining various metal dopants have started back in 1960s, and various emerging technologies and having a high Bi content different methods were used, including Pulsed Laser Depo- and also other metal-atom dopants like Ga or Al within the sition (PLD), Liquid Phase Epitaxy (LPE), Ion Beam Sput- garnet structure. The physical properties (optical, magnetic, tering (IBS), Reactive Ion Beam Sputtering (RIBS), Sol-gel and MO) of all garnet materials depend significantly not only process, and RF magnetron sputtering [1–9]. Bi:IGs are still on the Bi content and the substitution of other extra atoms considered to be the best magneto-optic (MO) material and dopants within the sublattices of the garnet structure, type among all known semitransparent materials and are but also on the multiple process parameters relevant to the therefore of interest for various optical, MO, and other synthesis of Bi:IGs [3]. The synthesis of high-quality Bi:IG applications. The extraordinary MO properties of highly Bi- thin film materials is usually a very complex and multi- substituted iron garnet materials allow the modulation of the step process sequence which also requires complex multipa- polarisation state and intensity of polarized light by means rameter process optimizations applied at both the deposition 2 Advances in Optical Technologies and annealing stages. RF magnetron sputtering using low- 2.2. Oven Annealing Heat Treatment. The as-deposited films pressure (1–5 mTorr) argon (Ar) plasma is one of the most (amorphous-phase layers) were placed into a conventional flexible approaches to deposit MO garnet materials. The abil- box-furnace-type oven annealing system to anneal them ity to vary the substrate temperature during the deposition in air atmosphere using the appropriate composition-de- and also the possibility of growing the films on relatively cold pendent optimized isothermal crystallization regimes. The substrates are very important for the integration of Bi:IG annealing processes were run to crystallize the sputtered thin films into optical devices. We prepare highly Bi-substituted films inside the oven with temperature ramp rates (up and dysprosium (or lutetium) iron garnet thin films using RF down) in between 3–5 C/min, for a number of different sputtering followed by the conventional (postdeposition) annealing durations. We used low rates of temperature ramp- oven annealing in air atmosphere. Our MO garnet thin film ing during the annealing processes for our garnet-oxide materials are highly competitive (in terms of MO figure of composite materials to avoid the film surface degradation merit) with all other garnet materials synthesized to date by and microcrack formation in samples. We found that the using various modern microfabrication technologies. optimization of annealing regimes (both temperature and In this paper, we report on the physical properties and annealing process durations were optimized) for our highly behaviour (especially the magnetic switching behaviour) Bi-substituted garnet materials was strongly dependent on of several RF-sputtered high-performance, highly bismuth- the composition of films. Figure 2 shows a photograph of substituted ferrimagnetic garnet materials which are suitable (150 W Bi Dy Fe Ga O +30W Bi O , or having 2 1 4.3 0.7 12 2 3 for integration into various photonic devices and for many 37 vol.% of excess Bi O ) composite films on Corning 1737 2 3 magneto-optic applications. glass (larger sample) and on a GGG (smaller sample) sub- strate having hazy and optically damaged (scatterer-type) 2. Experimental surfaces due to over-annealing. These films were annealed in air atmosphere for only 30 minutes at 520 C, with 2.1. RF Sputtering Processes and Thin Film Growth. Highly a temperature ramp (up/down) rate of 5 C/min. However, bismuth-substituted garnet films and also various cosput- this amount of thermal exposure was already excessive, due tered nanocomposite garnet-bismuth oxide thin films were to the rather high bismuth content of the deposited layers. fabricated by using RF magnetron sputtering system (Korea It is evident that either the annealing temperature or the Vacuum Technology Ltd KVS-T 4065). The garnet and annealing duration or both were not optimized to form opti- composite garnet-oxide thin films of different thicknesses cally flat nanocrystalline layers from the amorphous phase of (up to 1500 nm) were prepared in a high-vacuum chamber these garnet-oxide composites. So it is one of the important using low-pressure argon (Ar) plasma at different sub- factors of garnet thin films synthesis to find an optimized strate temperatures ranging between 250–680 C during the annealing regimes as the optical and MO properties are deposition. We prepared several batches of garnet thin vitally related to the optimization of the annealing regimes. films and also garnet-bismuth oxide composite films having Even though these films were optically spoiled, they still did different volumetric contents of Bi O added by cosputtering 2 3 demonstrate some useful MO properties in terms of Faraday from a separate target. The nominal stoichiometries of the rotation per unit film thickness as reported in a previous sputtering targets Bi Dy Fe Ga O (where m = 2and m 3−m 5−n n 12 publication [10]. n = 1 and 0.7) and Bi Lu Fe Al O (where a = 1.2 a 3−a 5−b b 12 and b = 1.4) based on high-purity (99.99%) oxide material 2.3. Thin-Film Materials Characterization. The structural, mixes were selected to experiment with different levels optical, magnetic, and MO properties of high-quality an- of magnetostriction-induced uniaxial magnetic anisotropy. nealed garnet thin films were subjected to characterization A separate Bi O target was used as an external source 2 3 using a number of characterization techniques. The crystal of Bi oxide (and also Bi) content for incorporation into structure and impurity phases of garnet and garnet-bismuth the nanocomposite materials during cosputtering processes. oxide thin films of type (BiDy) (Fe,Ga) O have been ana- A schematic diagram of our cosputtering geometry is shown 5 lyzed using X-ray diffractometry (XRD) data generated by in Figure 1 (up to two guns were used concurrently in Panalytical XPert Pro X-ray diffractometer configured for our experiments). The target materials (garnet and oxide) near-grazing-incidence powder diffraction measurements of 3 diameter were placed at three RF guns of the using the CuK (λ = 0.15406 nm) radiation. The optical down-sputtering system having about 18 cm of source- α1 properties of garnet films were investigated by variable- to-substrate separation. All the guns with independently angle spectroscopic ellipsometry and also by deriving the activated shutters are placed at the corners of the equilateral absorption coefficient spectra, while the measurements of triangle and tilted towards the substrates. The substrates’ Faraday rotation hysteresis loops revealed the most impor- stage rotation was adjusted to be near 40–50 rpm during tant magnetic and MO properties of the garnet films. The the deposition processes to provide a good deposition thickness/composition uniformity of sputtered films on all specific Faraday rotation measurements were performed al- most across the entire visible spectral region by using substrates. The film thicknesses were always measured in two ways; thicknesses were monitored during the deposition and several laser light sources, a Thorlabs PAX polarimeter and also remeasured after deposition using the spectrally best- an electromagnet. A transmission-mode polarizing micro- fitted transmission spectra and also their measured refractive scope (Leitz Orthoplan) was used to observe the magnetic index and absorption spectra. domain patterns of garnet films. Gun3 (Bi, Lu) (Fe, Al) O 5 12 Advances in Optical Technologies 3 Gun 2 RF power Bi O 2 3 Bi O (Bi, Dy, Lu) (Fe, Ga, Al) O 2 3 3 5 12 Ar plasma (BiLu) (FeAL) O :Bi O 3 5 12 2 3 film (amorphous) Amorphous 6R Amorphous film 4R 8R 10R (BiDy) (FeGa) O :Bi O 3 5 12 2 3 Heat treatment film (annealed) Crystal Crystallized film Substrate (a) (b) Figure 1: (a) Schematic diagram of the cosputtering system geometry, (b) flow chart of garnet-bismuth oxide cosputtered thin films processing. We have previously not only reported on the optical and magneto-optical properties of the sputtered (Bi, Dy) (Fe, Ga) O material type and its nanocomposite 5 12 derivativesoftype(Bi,Dy) (Fe, Ga) O :Bi O but also doc- 12 2 3 3 5 umented their annealing behaviour and the effects of thermal exposure on the resulting optical and MO properties [10, 16]. We have also reported on the synthesis of RF-sputtered garnet materials of composition type Bi Lu Fe Al O 1.8 1.2 3.6 1.4 12 Figure 2: Photographs of a correctly annealed garnet-oxide com- for the first time, and we believe that no physical vapour posite thin film and two over-annealed films of composition type deposition methods have so far been used previously to Bi Dy Fe Ga O :Bi O sputtered onto Corning 1737 (larger 2 1 4.3 0.7 12 2 3 synthesize this material type with a high Bi-content (near samples) and GGG (smaller sample) substrates. The transparent two formula units) [17]. The codeposited nanocomposite film (on the left) has a smaller thickness and high surface quality. derivatives of type (Bi, Lu) (Fe, Al) O :Bi O have been 12 2 3 The two over-annealed films were oven treated at 520 C for 30 min. 3 5 under investigation, and the detailed results will be reported elsewhere soon. The addition of excess Bi O to the base 2 3 garnet composition of type Bi Lu Fe Al O during 1.8 1.2 3.6 1.4 12 cosputtering did not have much influence on the Faraday 3. Results and Discussion rotation of the garnet layers but significantly reduced the The correctly annealed highly Bi-substituted magneto-optic optical absorption. The garnet-oxide composite films of type doped-iron-garnet thin films demonstrated excellent optical (Bi, Lu) (Fe, Al) O :Bi O (4.5 vol.% extra bismuth oxide) 3 5 12 2 3 properties across the visible and near-infrared spectral range. possessed extremely large MO figure of merit (more than 50 We observed very similar behaviours of the optical absorp- at 635 nm), which was more than three times higher than tion spectra in both types of our sputtered garnet films that of the typical garnet layer (Figure 4). Figure 4. shows (dysprosium iron garnets and lutetium iron garnets). It is the values of the specific Faraday rotation achieved and MO important to note that lower absorption coefficients were figures of merit measured using 532 nm and 635 nm light. always observed (as was expected) in the cosputtered garnet- The X-ray diffraction patterns of Bi Dy Fe Ga O and 2 1 4 1 12 bismuth oxide composite thin films compared to the absorp- (BiDy) (FeGa) O :Bi O layers synthesized on glass sub- 12 2 3 tion of typical (stoichiometrically deposited) garnet layers. strates are presented in Figure 5. The data reveals the nano- Figure 3 shows the absorption coefficient spectra measured crystalline microstructure of the annealed garnet materials in typical (Bi, Dy, Lu) (Fe, Ga, Al) O garnet layers and also and the body-centered cubic lattice structure type, as well as 5 12 those measured in the best-performing cosputtered garnet- only one identifiable impurity phase (Fe O ) being present. 3 4 oxide (Bi, Dy, Lu) (Fe, Ga, Al) O :Bi O composite layers The addition of extra Bi O always reduced the relative inten- 12 2 3 2 3 sputtered onto GGG (111) substrates. Similar trends in the sities of the iron-oxide diffraction peaks, as witnessed by the absorption coefficient spectra were also observed in the films diffraction datasets of the films synthesized by cosputtering. sputtered onto the glass (Corning 1737) substrates. This indicates the presence of less iron oxide outside Gun 1 (Bi, Dy) (Fe, Ga) O 5 12 4 Advances in Optical Technologies 500 550 600 650 Wavelength (nm) Typical Bi Dy Fe Ga O garnet film on GGG, annealed for 1 hr at 680 C 2 1 4.3 0.7 12 Typical Bi Dy Fe Ga O garnet film on GGG, annealed for 1 hr at 700 C 2 1 4 1 12 Typical Bi Lu Fe Al O garnet film on GGG, annealed for 1 hr at 650 C 1.8 1.2 3.6 1.4 12 Bi Dy Fe Ga O :Bi O (est. 23.6 vol%) composite on GGG, annealed for 1 hr at 560 C 2 1 4.3 0.7 12 2 3 Bi Dy Fe Ga O :Bi O (est. 23.3 vol%) composite on GGG, annealed for 2 hrs at 580 C 2 1 4 1 12 2 3 Bi Lu Fe Al O :Bi O (est. 4.5 vol%) composite on GGG, annealed for 10 hrs at 610 C 1.8 1.2 3.6 1.4 12 2 3 Figure 3: Derivedabsorptioncoefficient spectra of the best-performing garnet layer types and these of the garnet-oxide composite (having different vol.% content of excess Bi O ) films deposited onto GGG (111) substrates. 2 3 50 10 40 8 30 6 20 4 10 2 0 0 Composite type 532 nm MO figure of merit 635 nm MO figure of merit Faraday rotation at 532 nm Faradayrotationat635nm Figure 4: Summary of the measured specific Faraday rotation data (dashed lines) and MO figures of merit (bar diagrams) of different garnet and garnet-oxide composite layer types; the highest values (of the specific Faraday rotation and MO figure of merit) achieved in our experiments so far are indicated. the garnet nanocrystallites. No diffraction peaks character- The effects of extra bismuth oxide incorporation on the istic of Bi O have been observed since the bismuth oxide MO properties were investigated, and also the influence 2 3 remained in its amorphous phase even after the annealing of the volumetric content of extra bismuth oxide was ob- treatments. served (Figure 6(a)). Our experimental results revealed Figure 6 shows the hysteresis loops of specific Faraday that by controlling the volumetric content of extra Bi O 2 3 rotation at 532 nm measured in several best-performing gar- it was possible to control (to some degree) the magnetic net-bismuth oxide nanocomposite films, which had different switching behaviour and the coercive force value of garnet- coercive force, saturation field, and switching field values. oxide nanocomposite media. This type of control over the −1 Absorption coefficient (cm ) MO figure of merit (degs) (BiDy) Fe Ga O 3 4 1 12 1.9 9.5 garnet 14.5 24.2 (BiDy) Fe Ga O + 3 4 1 12 23.3 vol% Bi O 2.6 2 3 9.8 25.7 composite 42.5 (BiDy) Fe Ga O 3 4.3 0.7 12 1.1 garnet 7.9 11.4 (BiDy) Fe Ga O + 3 4.3 0.7 12 1.6 23.6 vol% Bi O 2 3 10.1 29.2 composite 22.1 (BiLu) (FeAl) O 3 5 12 1.6 5.8 garnet 13.9 15.7 (BiLu) (FeAl) O + 3 5 12 6.1 1.7 4.5 vol% Bi O 2 3 22.1 composite 50.2 Specific Faraday rotation (deg/µm) Advances in Optical Technologies 5 (420) (422) Fe O 3 4 (642) Bi Dy Fe Ga O :Bi O composite film on glass, annealed at 580 C 2 1 4 1 12 2 3 (211) (400) (640) Fe O 3 4 (842) (444) (800) 600 (220) Bi Dy Fe Ga O :Bi O composite film on glass, annealed at 560 C 2 1 4.3 0.7 12 2 3 (321) Fe O 3 4 (521) Bi Dy Fe Ga O film on galss, annealed at 620 C 2 1 4 1 12 10 20 30 40 50 60 70 80 2Θ (degs) Figure 5: X-ray diffraction patterns of several sputtered Bi-substituted thin-film garnet materials deposited onto glass substrates. 6 4 −1500 −1000 −500 500 1000 1500 −2500 −1500 −500 500 1500 2500 −1 6 Hc = (45 ± 5) Oe −2 5 and Hsat = 350 Oe −2 Hc Hc == (30 (30 ±± 5 5)) O Oee and and H Hsat sat == 270 270 O Oee 2 −4 −3 −400 −300 −200 −100 100 200 300 400 −4 −1 −6 −2 −3 −5 −4 −5 −8 −6 −6 Magnetic field (Oe) −7 −10 Magnetic field (Oe) Magnetic field (Oe) Typical Bi Lu Fe Al O garnet film Bi Dy Fe Ga O :Bi O composite 1.8 1.2 3.6 1.4 12 2 1 4 1 12 2 3 on GGG; Hc = (45 ± 5) Oe (about 22 vol% excess oxide) on GGG Composite Bi Lu Fe Al O :Bi O 1.8 1.2 3.6 1.4 12 2 3 Bi Dy Fe Ga O :Bi O composite 2 1 4 1 12 2 3 (4.5 vol%) film on GGG; Hc = (30 ± 5) Oe (about 20 vol% excess oxide) on GGG (a) (b) Figure 6: Hysteresis loops of specific Faraday rotation measured using a 532 nm laser source in several highly Bi-substituted iron garnet- bismuth oxide nanocomposite films of types (a) (BiDy) (FeGa) O :Bi O and (b) (BiLu) (FeAl) O :Bi O , deposited onto GGG (111) 5 12 2 3 3 5 12 2 3 substrates. magnetic properties can lead towards achieving tunability in [13]. On the other hand, rather low coercive force values magneto-photonic crystals, which is very essential for dif- were measured in the second type of thin film materials ferent types of applications including the optical isolators studied (bismuth-substituted lutetium iron garnets doped and optical polarization controllers. The experimental setup with aluminium) sputtered onto GGG (111) substrates. The for characterization of magneto-optic switching response measured coercive force for the films on GGG substrates as well as magnetization dynamics has been described in was about 45 Oe, whereas the addition of extra bismuth [20]. Nanosecond-range switching response times of below oxide into the films reduced the coercivity of the films 20 ns were measured previously in 1∼2 μm thick highly as indicated in the inset (Figure 6(b)). We measured a Bi-substituted iron garnet films of composition type high Faraday-effect magnetic field sensitivity within the (Bi, Dy) (Fe, Ga) O . Note that the high-speed switch- linear range of magnetizations of up to 42.8 /(cm·Oe) at 5 12 ing time constant of 2.4 ns has also been measured in 635 nm, which was higher than that obtained previously Bi Fe Ga O garnet films of 1 mm aperture size at 532 nm in epitaxial (BiLu) (FeGa) O films prepared by LPE [18]. 3 4 1 12 12 3 5 Specific Faraday rotation (deg/micron) Intensity (a.u.) Faraday rotation (deg/µm) MO ultrafast switches Garnet waveguides development Magnetic field sensors 6 Advances in Optical Technologies 20 µm 20 µm (a) (b) Figure 7: Magnetic domain patterns obtained in two different garnet-bismuth oxide composite thin films (a) Bi Dy Fe Ga O :Bi O , with 2 1 4 1 12 2 3 an est. 23% of excess oxide, and (b) Bi Lu Fe Al O :Bi O , with an est. 4.5% of excess bismuth oxide sputtered onto GGG (111) 1.8 1.2 3.6 1.4 12 2 3 substrates. and possess a significant in-plane magnetization component which will be especially suitable for the development of gar- net waveguides, nonreciprocal integrated optics components as well as the magnetic field imaging and sensing devices. 4. Applications of RF-Sputtered Garnet Materials MO garnet MO spatial light MO imaging Modern civilization demands superior technologies and materials modulators devices high-speed communication systems for achieving a better lifestyle. It is the challenge for modern science and tech- nology to serve the requirements of society by providing all required technological facilities through new research, inven- tions, and reconfiguration of the existing devices and tech- nologies. Materials science is one of the branches of science that can achieve rapid progress in research and applications for many new and existing technologies. A wide and growing range of applications require the design and development Figure 8: The existing and potential new application areas of MO of new photonic materials (including MO garnet materials) garnet materials. which can enable control over the interaction of light with matter. MO garnet materials, especially the Bi-substituted iron garnet compounds are very suitable for various applica- We also measured even lower coercive force values of less tions (Figure 8) including lightwave polarization controllers, than 20 Oe in thin films sputtered onto GGG at high MO flaw detection, high-density magnetic recording and substratetemperaturesnear680 C. MO data recovery, high-speed spatial and temporal light The magnetic domain structures observed in our two modulators, magnetic nanostructures for ultracold atoms different types of garnet-bismuth oxide composite thin films trapping, and the development of magnetic photonic crystals in the absence of externally applied magnetic fields are (MPCs). The combination of the remarkable properties of shown in Figure 7. The domain patterns were observed using magnetic garnet materials shows great promise for applica- a transmission-mode polarizing microscope. tions in next-generation integrated optics, nanophotonics, The combination of physical properties of the highly and also in reconfigurable photonics. The development of Bi-substituted iron garnets of both types shows a great new garnet-type materials by synthesizing Bi-substituted promise for the future development of different emerging iron garnets and their codeposited nanocomposite garnet- types of integrated and reconfigurable nanophotonic devices. oxide derivatives will not only allow the integration of Garnet thin films of type (BiDy) (FeGa) O demonstrated garnet-based components into existing integrated-optics 3 5 simultaneously a record high MO quality, and strong uni- manufacturing processes, but will also help achieve cost axial magnetic anisotropy will be attractive for visible-range efficiency by providing the functional materials which are and near-infrared applications, including the development technologically compatible with the presently used material of high-performance magnetic field visualizers and inte- combinations. That will have influence on numerous com- grated optical polarization controllers. The garnet films of munities, because most of the innovative technologies using type (BiLu) (FeAl) O feature magnetically soft behaviour these advanced materials will be easy to implement and less 3 5 Nonreciprocal devices MO circulator anddeflectors Magnetic component of MPCs Advances in Optical Technologies 7 costly. [8] Y. Zhang, X. Wang, H. Xia et al., “Characterization of Bi- substituted dysprosium iron garnet films prepared Sol-gel process,” Journal of Materials Sciences and Technology, vol. 20, no. 1, pp. 66–68, 2004. 5. Conclusions [9] M. Vasiliev, M. Nur-E-Alam, V. A. Kotov et al., “RF magnetron sputtered (BiDy) (FeGa) O :Bi O composite garnet-oxide We have synthesized a range of bismuth-substituted iron gar- 3 5 12 2 3 materials possessing record magneto-optic quality in the visi- net thin-film materials having different bismuth substitution ble spectral region,” Optics Express, vol. 17, no. 22, pp. 19519– levels and metal dopants using the RF magnetron sputtering 19535, 2009. technique, which is one of the most common physical vapour [10] M. Nur-E-Alam, M. Vasiliev, and K. Alameh, “Nano-struc- deposition methods. We have characterized the nanocrys- tured magnetic photonic crystals for magneto-optic polar- talline thin-film garnet materials crystallized using high-tem- ization controllers at the communication-band wavelengths,” perature oven processing and found the ways of achieving Optical and Quantum Electronics, vol. 41, no. 9, pp. 661–669, low optical absorption losses, relatively high specific Faraday rotation, and also some control over the magnetic switching [11] A. Abdelrahman, M. Vasiliev, K. Alameh, and P. Hannaford, behaviour. Our newly synthesized MO materials of two dif- “Asymmetrical two-dimensional magnetic lattices for ultra- ferent composition types possess record high MO figures of cold atoms,” Physical Review A, vol. 82, no. 1, Article ID 012320, 6 pages, 2010. merit in conjunction with other excellent physical properties [12] I. L. Lyubchanskii, N. N. Dadoenkova, M. I. Lyubchanskii, E. which are attractive for use in various integrated-optics and A. Shapovalov, and T. Rasing, “Magnetic photonic crystals,” photonics applications. Journal of Physics D, vol. 36, no. 18, pp. R277–R287, 2003. [13] S. Kang, S. Yin, V. Adyam, Q. Li, and Y. Zhu, “Bi Fe Ga O 3 4 1 12 garnet properties and its application to ultrafast switching in Acknowledgments the visible spectrum,” IEEE Transactions on Magnetics, vol. 43, no. 9, pp. 3656–3660, 2007. The authors would like to acknowledge the support of the [14] T. Kim, S. Nasu, and M. Shima, “Growth and magnetic behav- Faculty of Computing, Health and Science, Edith Cowan ior of bismuth substituted yttrium iron garnet nanoparticles,” University, Australia, and the Department of Nanobio Mate- Journal of Nanoparticle Research, vol. 9, no. 5, pp. 737–743, rials and Electronics, Gwangju Institute of Science and Tech- nology, Republic of Korea. They would also like to pay special [15] M. Vasiliev, M. Nur-E-Alam, K. Alameh et al., “Annealing thanks to the Materials Characterization Lab, Korea Optical behaviour and crystal structure of RF-sputtered Bi-substituted Technology Institute (KOPTI, Gwangju, South Korea) for dysprosium iron-garnet films having excess co-sputtered Bi- performing the XRD data acquisition. oxide content,” Journal of Physics D, vol. 44 , article 075002, no. 7, 2011. [16] M. Nur-E-Alam, M. Vasiliev, K. Alameh, and V. Kotov, “High-quality RF-sputtered magneto-optic garnet films of References Bi Lu Fe Al O with low coercivity for applications in 1.8 1.2 3.6 1.4 12 [1] C. F. Buhrer, “Faraday rotation and dichroism of bismuth cal- integrated optics, imaging and sensing devices,” in Proceed- cium vanadium iron garnet,” Journal of Applied Physics, vol. ings of the International Conference on High-capacity Optical 40, no. 11, pp. 4500–4502, 1969. Networks and Enabling Technologies Conference,Cairo,Egypt, December 2010. [2] G.B.Scott andD.E.Lacklison,“Magnetooptic properties [17] N. 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