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Dongquoc, Viet,Kuchi, Rambabu,Van, Phuoc Cao,Yoon, Soon-Gil,Jeong, Jong-Ryul Elsevier 2018 CURRENT APPLIED PHYSICS Vol.18 No.2
<P>This work investigated the effects of heating rate and annealing on the magneto-optical properties of bismuth-substituted yttrium iron garnet (Bi-YIG) thin films on glass and (111)-oriented single-crystalline gadolinium gallium garnet (GGG) substrates fabricated by metal-organic decomposition (MOD). We modified the MOD method by eliminating the pre-annealing process. We performed annealing at various temperatures to determine the optimal temperature for obtaining the Bi-YIG phase. We then annealed at the optimized temperature using various heating rates. The optimal conditions were annealing for 1 h at 750 degrees C at a heating rate of 30 degrees C/min on GGG to obtain highly crystallized fine grains. The Faraday rotation for this film was about -10.5 degrees/mu m. The optimized heating rate enhanced the magneto-optical properties due to improved crystallinity and saturated magnetization. The Bi-YIG thin films prepared by this prescribed MOD method exhibited excellent magneto-optical performance and are potential candidates for applications in optical devices. (c) 2017 Elsevier B.V. All rights reserved.</P>
Dongquoc, Viet,Kuchi, Rambabu,Van, Phuoc Cao,Surabhi, Srivathsava,Lee, Sung Woo,Kim, Dongsoo,Jeong, Jong-Ryul Elsevier 2019 Ceramics international Vol.45 No.16
<P><B>Abstract</B></P> <P>A bismuth-substituted yttrium iron garnet (Bi-YIG) thin film on a glass substrate with high magneto-optical (MO) performance was fabricated using metal-organic decomposition (MOD). To enhance the MO performance of the as-grown Bi-YIG thin film, different amounts of polyvinylpyrrolidone (PVP) were introduced to a metal nitrate precursor solution as a reducing agent and growth modifier. By using the optimized concentration, we have obtained a Bi-YIG thin film that exhibited good morphology, high crystallinity, and high saturation magnetization. The Faraday rotation (FR) angle of this film reached its highest value of −8.0°/μm, which is close to that of thin films fabricated on gadolinium gallium garnet substrates (−10.5°/μm). Moreover, Bi<SUB> <I>x</I> </SUB>Y<SUB>3−<I>x</I> </SUB>Fe<SUB>5</SUB>O<SUB>12</SUB> films with different Bi substitutions were synthesized; these films showed a higher FR angle, of up to −12.0°/μm (Bi<SUB>2.5</SUB>Y<SUB>0.5</SUB>Fe<SUB>5</SUB>O<SUB>12</SUB>), in which the peak position of the FR angle resided in the visible range (505–540 nm). This work reveals that high-quality Bi-YIG thin films on glass substrates via MOD are promising for MO device applications.</P>
Viet Dongquoc,Rambabu Kuchi,Phuoc Cao Van,윤순길,정종율 한국물리학회 2018 Current Applied Physics Vol.18 No.2
This work investigated the effects of heating rate and annealing on the magneto-optical properties of bismuth-substituted yttrium iron garnet (Bi-YIG) thin films on glass and (111)-oriented single-crystalline gadolinium gallium garnet (GGG) substrates fabricated by metal-organic decomposition (MOD). We modified the MOD method by eliminating the pre-annealing process. We performed annealing at various temperatures to determine the optimal temperature for obtaining the Bi-YIG phase. We then annealed at the optimized temperature using various heating rates. The optimal conditions were annealing for 1 h at 750 °C at a heating rate of 30 °C/min on GGG to obtain highly crystallized fine grains. The Faraday rotation for this film was about −10.5°/μm. The optimized heating rate enhanced the magneto-optical properties due to improved crystallinity and saturated magnetization. The Bi-YIG thin films prepared by this prescribed MOD method exhibited excellent magneto-optical performance and are potential candidates for applications in optical devices.
Rambabu Kuchi,Viet Dongquoc,김도진,윤순길,박성용,정종률 대한금속·재료학회 2017 METALS AND MATERIALS International Vol.23 No.2
In this work, we report on the large-scale room-temperature synthesis of Co superstructures using a facile liquidphase reduction method in an aqueous medium. This method yielded pure Co powders within a short periodof time without the use of any surfactants. The morphological changes in the Co superstructures could becontrolled simply by varying the amounts of reducing agent (hydrazine hydrate). The morphology of theCo powders systematically controlled from aggregated foliage to isolated microfoliage by increasing thehydrazine hydrate addition from 4 ml to 8 ml. The morphology-dependent electromagnetic properties, includingthe electric permittivity, and magnetic permeability, were investigated over the microwave frequencyrange, 2-18 GHz. Co isolated microfoliage showed a maximum reflection loss (RL) of -32 dB at 9 GHz with amatching thickness of 2.5 mm, whereas the aggregated foliage Co superstructures displayed a maximum RLof -17 dB at 11 GHz with a matching thickness of 2.5 mm. The stronger absorption for isolated microfoliagewas ascribed to a continuous micro networks and vibrating microcurrent dissipation arise from size and shapeof the isolated microfoliage. The calculated RL suggested that the as-prepared samples were potential microwaveabsorption candidates in the X-band region.