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Early Stage Report: Graduate Research

Magnetically Directed Percolation Networks in Polydopamine-Mediated Carbon Nanotube/Fe3O4 Nanocomposites
Dongyeong Gim, Hyeokju Kwon, Minjeong Ha
J Electr Electron Mater 2026;39(3):288-294.
Published online May 1, 2026
DOI: https://doi.org/10.4313/JEEM.2026.39.3.8
Polymer nanocomposites incorporating inorganic nanofillers have emerged as highly promising electromagnetic interference (EMI) shielding materials, combining mechanical compliance with robust conductive percolation networks. Carbon nanotubes (CNTs) are particularly attractive as conductive fillers because their high aspect ratio facilitates percolation at low loadings. Also, CNTs offer superior mechanical durability under deformation compared to rigid, fracture-prone metal nanowires. For EMI shielding, high electrical conductivity is critical as it enhances both reflection and absorption through efficient charge dissipation and conduction losses. However, achieving highly aligned conductive pathways without degrading the intrinsic electrical properties of CNTs remains a significant challenge. Here, we demonstrate a non-destructive magnetic surface-functionalization and alignment strategy. Using a polydopamine (PDA)-mediated route, pristine multiwalled CNTs are uniformly decorated with Fe3O4 nanoparticles (FMWCNTs). This enables highly effective magnetic field-driven alignment at fields as low as 10 mT, promoting the strategic formation of percolation networks. By optimizing the Fe₃O₄/MWCNT ratio for high saturation magnetization and uniform coverage, the aligned FMWCNTs exhibit significant electrical anisotropy, delivering a 10.7-fold higher electrical conductivity in the parallel configuration compared to the vertical configuration. These findings present a scalable, room-temperature platform for engineering directionally enhanced conductivity in polymer nanocomposites, with broad applicability in advanced EMI shielding, flexible electronics, and advanced packaging technologies.
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e investigated the effects of post-annealing in vacuum, nitrogen, and hydrogen atmospheres on the structural, electrical, and optical properties of 600 nm thick Al-doped ZnO (ZnO:Al) thin films deposited by RF magnetron sputtering at room temperature. Post-annealing in hydrogen atmosphere at 400℃ for 1 hour showed the most significant improvement in electrical properties. Resistivity decreased from 9.11×10⁻³ to 1.4×10⁻³ Ω·cm, electron mobility increased from 4.11 to 18.23 cm²/V·s, and electron carrier concentration increased from 1.63×10²⁰ to 4.85×10²⁰ cm⁻³. In contrast, post-annealing in vacuum and nitrogen atmospheres resulted in degraded electrical properties due to oxygen and nitrogen chemisorption at grain boundaries. The enhancement in hydrogen-annealed films was attributed to the formation of additional oxygen vacancies and desorption of adsorbed oxygen species from grain boundaries. All films maintained excellent optical transparency of 80-90% in the visible range. The optical bandgap exhibited a blue-shift from 3.365 eV to 3.624 eV due to the Burstein-Moss effect induced by the increased electron carrier concentration. These results confirmed that hydrogen atmosphere post-annealing is the most effective method for enhancing the electrical conductivity of ZnO:Al thin films while maintaining high optical transparency.
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Fabrication and Characterization of Magnetic Field Sensor Based on Fiber Bragg Grating and Terfenol-D Bar
Kwang Taek Kim, Gun Pyo Kim
J Electr Electron Mater 2025;38(3):278-281.   Published online May 1, 2025
DOI: https://doi.org/10.4313/JKEM.2025.38.3.6
We have proposed and demonstrated a fiber optic magnetic field sensor using a FBG (fiber bragg grating) attached on a Terfenol-D bar. The volume of Terfenol-D is changed by the applied magnetic field due to the magnetostriction effect, as a result, the grating period of FBG varies with the intensity of the magnetic field and the Bragg wavelength of FBG is shifted. The temperature sensitivity of the sensor was measured with and without the magnetic field. The temperature sensitivity of the sensor was measured to be 0.02 nm/℃. We observed that the sensitivity of the fabricated device to magnetic field intensity was decreased with the environment temperature.
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Synthesis of Monodisperse Iron Oxide Nanoparticles with Control of Surface Properties and Magnetization
Dongyeong Gim, Hyeokju Kwon, Minjeong Ha
J Electr Electron Mater 2025;38(1):89-94.   Published online January 1, 2025
DOI: https://doi.org/10.4313/JKEM.2025.38.1.12
Iron oxide nanoparticles (NPs) have gained significant attention for their broad applicability in biomedical imaging, soft robotics, and catalysis owing to their exceptional magnetic properties and biocompatibility. A key challenge in maximizing their functionality lies in achieving a uniform size distribution and dispersity, alongside strong interfacial affinity with the surrounding medium that are essential for optimizing magnetic behavior and processibility. In this study, we present a facile solvothermal synthesis of monodisperse iron oxide NPs with tunable size and controllable surface hydrophobicity by varying precursors, capping agents, and solvents. By varying these synthesis parameters, we demonstrate a clear correlation between NP size, dispersity, and key magnetic properties, including saturation magnetization (MS) and coercivity (HC). This advancement in synthesis methodology offers a reliable, efficient approach for producing high-quality iron oxide NPs, which makes possible for practical use of them across a range of technological and biomedical applications.
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Fabrication of YBCO Superconducting Bulk Magnets
Sang Heon Lee
J Electr Electron Mater 2024;37(4):407-411.   Published online July 1, 2024
DOI: https://doi.org/10.4313/JKEM.2024.37.4.7
In this study, we fabricated single grain YBCO bulk superconductors with control of the distance between the seed and the upper surface of the YBCO compacts. The magnetic levitation force of the YBa2Cu3O7 superconducting bulk, which corresponds to the energy amount of the superconducting bulk, was measured to be 32.634 N at the center of the bulk where the seed was placed. Under field cooling conditions, a capture magnetic force of 2.17 kG was observed at the center of the bulk. The trapped magnetic force curve corresponding to the stability of the superconducting bulk means that the superconducting specimens were well grown in the form of single grains.
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Effect on the Thermal Treatment for Improving Efficiency in Silicon Heterojunction Solar Cells
Hyeong Gi Park, Junsin Yi
J Electr Electron Mater 2024;37(4):439-444.   Published online July 1, 2024
DOI: https://doi.org/10.4313/JKEM.2024.37.4.12
This study investigates the post-thermal treatment effects on the efficiency of silicon heterojunction solar cells, specifically examining the influence of annealing on p-type microcrystalline silicon oxide and ITO thin films. By assessing changes in carrier concentration, mobility, resistivity, transmittance, and optical bandgap, we identified conditions that optimize these properties. Results reveal that appropriate annealing significantly enhances the fill factor and current density, leading to a notable improvement in overall solar cell efficiency. This research advances our understanding of thermal processing in siliconbased photovoltaics and provides valuable insights into the optimization of production techniques to maximize the performance of solar cells.
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Magneto-Mechano-Triboelectric Generator Enabled by Ferromagnetic-Ferroelectric Composite
Yeseul Lim, Geon-tae Hwang
J Electr Electron Mater 2024;37(1):112-117.   Published online January 1, 2024
DOI: https://doi.org/10.4313/JKEM.2024.37.1.16
The Internet of Things (IoT) device is a key component for Industry 4.0, which is the network in homes, factories, buildings, and infrastructures to monitor and control the systems. To demonstrate the IoT network, batteries are widely utilized as power sources, and the batteries inevitably require repeated replacement due to their limited capacity. Magneto-mechanoelectric (MME) generators are one of the candidate to develop self-powered IoT systems since MME generators can harvest electricity from stray alternating current (AC) magnetic fields arising from electric power cables. Herein, we report a magnetomechano- triboelectric generator enabled by a ferromagnetic-ferroelectric composite. In the triboelectric nylon matrix, a ferromagnetic carbonyl iron powder (CIP) was introduced to induce magnetic force near the AC magnetic field for MME harvesting. Additionally, a ferroelectric ceramic powder was also added to the MME composite material to enhance the chargetrapping capability during triboelectric harvesting. The final ferromagnetic-ferroelectric composite-based MME triboelectric harvester can generate an open-circuit voltage and a short-circuit current of 110 V and 8 μA, respectively, which were enough to turn on a light emitting diode (LED) and charge a capacitor. These results verify the feasibility of the MME triboelectric generator for not only harvesting electricity from an AC magnetic field but also for various self-powered IoT applications.
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Characteristics of Carbon-Doped Mo Thin Films for the Application in Organic Thin Film Transistor
Dong Hyun Kim, Yong Seob Park
J Electr Electron Mater 2023;36(6):588-593.   Published online November 1, 2023
DOI: https://doi.org/10.4313/JKEM.2023.36.6.8
The advantage of OTFT technology is that large-area circuits can be manufactured on flexible substrates using a lowcost solution process such as inkjet printing. Compared to silicon-based inorganic semiconductor processes, the process temperature is lower and the process time is shorter, so it can be widely applied to fields that do not require high electron mobility. Materials that have utility as electrode materials include carbon that can be solution-processed, transparent carbon thin films, and metallic nanoparticles, etc. are being studied. Recently, a technology has been developed to facilitate charge injection by coating the surface of the Al electrode with solution-processable titanium oxide (TiOx), which can greatly improve the performance of OTFT. In order to commercialize OTFT technology, an appropriate method is to use a complementary circuit with excellent reliability and stability. For this, insulators and channel semiconductors using organic materials must have stability in the air. In this study, carbon-doped Mo (MoC) thin films were fabricated with different graphite target power densities via unbalanced magnetron sputtering (UBM). The influence of graphite target power density on the structural, surface area, physical, and electrical properties of MoC films was investigated. MoC thin films deposited by the unbalanced magnetron sputtering method exhibited a smooth and uniform surface. However, as the graphite target power density increased, the rms surface roughness of the MoC film increased, and the hardness and elastic modulus of the MoC thin film increased. Additionally, as the graphite target power density increased, the resistivity value of the MoC film increased. In the performance of an organic thin film transistor using a MoC gate electrode, the carrier mobility, threshold voltage, and drain current on/off ratio (Ion/Ioff) showed 0.15 cm2/V·s, -5.6 V, and 7.5×104, respectively.
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Post-annealing Effect of NiO Thin Film Grown by RF Sputtering System on 4H-SiC Substrate
Soo-young Moon, Min-yeong Kim, Dong-wook Byun, Geon-hee Lee, Sang-mo Koo
J Electr Electron Mater 2023;36(2):170-174.   Published online March 1, 2023
DOI: https://doi.org/10.4313/JKEM.2023.36.2.10
Nickel oxide is a nonstoichiometric transparent conductive oxide with p-type conductivity, a wide-band energy gap of 3.4~4.0 eV, and excellent chemical stability, making it a very important candidate as a material for bipolar devices.P-type conductivity in Transparent Conductive Oxides (TCO) is controlled by the oxygen vacancy concentration. During the TCO film deposition process, additional oxygen diffusing into the NiO structure causes the formation of Ni 3p ions and Ni vacancies. This eventually affects the hole concentration of the p-type oxide thin film. In this work, the surface morphology and the electrical characteristics were confirmed in accordance with the annealing atmosphere of the nickel oxide thin film.
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Characteristics of VOx Thin Films Fabricated by Sputtering as Buffer Layer in Inverted Organic Solar Cell
Seong-soo Yang, Yong Seob Park
J Electr Electron Mater 2023;36(1):36-41.   Published online January 1, 2023
DOI: https://doi.org/10.4313/JKEM.2023.36.1.6
We investigated the properties of vanadium oxide (VOx) buffer layers deposited by a dual RF magnetron sputtering method under various target powers for inverted organic solar cells (IOSCs). Sputter fabricatged VOx thin films exhibited higher crystallinity with the increase of target power, resulting in a uniform and large grain size. The electrical properties of VOx films are improved with the increase of target power because of the increase of V content. In the results, the performance of IOSCs critically depended on the target power during the film growth because the crystalllinity of the VOx film affects the carrier mobility of the VOx film.
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Magnetic Force Properties of Superconducting Bulk
Sang Heon Lee
J Electr Electron Mater 2023;36(1):70-73.   Published online January 1, 2023
DOI: https://doi.org/10.4313/JKEM.2023.36.1.11
To improve superconductor properties, the size of the crystal grains of the superconductor should be adjusted, the amount of electricity flowing through the superconductor should be increased, and the superconductor should be designed to withstand external magnetic fields. It is necessary to control the microstructure so that many flux pinning centers are developed inside the superconductor so that defects are generated physically or chemically, and the micro secondary phase for trapped magnetic flux must be dispersed inside the superconductor. In order to measure the superconducting magnetic force of the superconducting bulk in a simplified manner, the superconducting magnetic force was analyzed using an Nd-Fe-B permanent magnet of 3.80 kG. In particular, by delaying the growth of partially melted Y2BaCuO5 particles, we devised a plan to refine Y2BaCuO5 particles to effectively improve superconducting magnetic force, and analyzed superconducting magnetic force in a single crystal YBa2Cu3O7-y superconducting bulk using a gauss meter. The melted superconducting bulk traps 80% or more of the applied magnetic field, and can be used as a bulk magnet of high magnetic field magnetization applicable to electric power equipment.
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Preparation of YBa2Cu3O7-y Superconductor Using Melt Method
Sang Heon Lee
J Electr Electron Mater 2022;35(6):622-625.   Published online November 1, 2022
DOI: https://doi.org/10.4313/JKEM.2022.35.6.12
YBa2Cu3O7-y bulk as a high temperature oxide superconducting conductor has the high critical temperature of 92 K. YBa2Cu3O7-y bulk superconductors have been fabricated by a seeded melting growth. Magnetic properties were studied by using superconductor of melted YBa2Cu3O7-y oxides. It was demonstrated that Y2BaCuO5 particles acts as a pinning center which plays an important role on the magnetic properties. The thickness of the upper and lower pellets of the YBa2Cu3O7-y bulk was formed at 40 mm with 55 g of the composition, and the YBa2Cu3O7-y superconductor was manufactured through a heat treatment process. Manufacturing the superconducting bulk, it is possible to improve the pore density of the superconducting bulk by providing a path through which oxygen could be emitted.
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Study of Pd Target Power Effects on Physical Characteristics of Pd-Doped Carbon Thin Films Using Dual Magnetron Sputtering Method
Young-chul Choi, Yong Seob Park
J Electr Electron Mater 2022;35(5):488-493.   Published online September 1, 2022
DOI: https://doi.org/10.4313/JKEM.2022.35.5.10
Generally, diamond-like carbon films (a-C:H, DLC) have been shown to have a low coefficient of friction, a high hardness and a low wear rate. Pd-doped C thin film was fabricated using a dual magnetron sputtering with two targets of graphite and palladium. Graphite target RF power was fixed and palladium target RF power was varied. The structural, physical, and surface properties of the deposited thin film were investigated, and the correlation among these properties was examined. The doping ratio of Pd increased as the RF power increased, and the surface roughness of the thin film decreased somewhat as the RF power increased. In addition, the hardness value of the thin film increased, and the adhesive strength was improved. It was confirmed that the value of the contact angle indicating the surface energy increases as the RF power increases. It was concluded that the increase in RF power contributed to the improvement of the physical properties of Pd-doped C thin film.
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Demonstration of Magnetoelectric Coupling Measurement at Off-Resonance and Resonance Conditions in Magnetoelectric Composites
Deepak Rajaram Patil, Jungho Ryu
J Electr Electron Mater 2022;35(4):333-341.   Published online July 1, 2022
DOI: https://doi.org/10.4313/JKEM.2022.35.4.3
Magnetoelectric (ME) composites are comprised of magnetostrictive and piezoelectric phases. Lots of theoretical and experimental works have been done on ME composites in the last couple of decades. The output performance of ME composites has been enhanced by optimizing the constituent phases, interface layer, dimensions of the ME composites, different operating modes, etc. However, the detailed information about the characterization of ME coupling in ME composites is not provided yet. Therefore, in this tutorial paper, we are giving an insight into the details of measurements of ME voltage coefficient of ME composites both at off-resonance and resonance conditions. A symmetric type Gelfenol/PMN-PZT/Gelfenol ME composites were fabricated by sandwiching (011) 32-mode PMN-PZT single crystal between two Galfenol plates by epoxy bonding are used for the example of ME coupling measurement. The details about the experimental setup used for the measurement of ME voltage coefficient are provided. Furthermore, a step-by-step measurement of ME voltage coefficient using computerized program is demonstrated. We believe the present experimental measurement details can help readers to understand the concept of ME coupling and its analysis.
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Frequency Dependent Magnetoelectric Responses in [0.948 Na0.5K0.5NbO3-0.052 LiSbO3]-[Co1-xZnxFe2O4] Particulate Composites
Moon Hyeok Choi, Byung Il Noh, Woosik Yun, Chaewon Jung, Su Chul Yang
J Electr Electron Mater 2022;35(3):303-307.   Published online May 1, 2022
DOI: https://doi.org/10.4313/JKEM.2022.35.3.14
Magnetoelectric (ME) properties of 3-0 type particulate composites have been investigated with respect to application features for reliable magnetic sensitivity and magnetically-induced output voltage. In order to figure out the magnetoelectric characteristics in the ME composites, frequency dependent ME responses were studied from [0.948 Na0.5K0.5NbO3-0.052 LiSbO3]-[Co1-xZnxFe2O4] (NKNLS)/Co1-xZnxFe2O4 (CZFO, x=0, 0.1, and 0.2). As a result, the maximal αME of 23.15 mV/cm·Oe was achieved from the NKNLS-CZFO (xZn = 0.1) composites at resonance frequency of 315 kHz and Hdc = 0 Oe. From the frequency dependent ME responses, it is clearly described that the self-biased ME composites can be used for applications as both magnetic sensors and energy harvesters, respectively.
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Investigation on Ferroelectric and Magnetic Properties of Pb(Fe1/2Nb1/2)O3 Fe-Site Engineered with Antisymmetric Exchange Interaction
Ji-hun Park, Ju-hyeon Lee, Jae-hyeon Cho, Jong Moon Jang, Wook Jo
J Electr Electron Mater 2022;35(3):297-302.   Published online May 1, 2022
DOI: https://doi.org/10.4313/JKEM.2022.35.3.13
We investigated the origin of magnetic behaviors induced by an asymmetric spin exchange interaction in Fe-site engineered lead iron niobate [Pb(Fe1/2Nb1/2)O3, PFN], which exhibits a room-temperature multiferroicity. The magnitude of spin exchange interaction was regulated by the introduced transition metals with a distinct Bohr magneton, i.e., Cr, Co, and Ni. All compositions were found to have a single-phase perovskite structure keeping their ferroelectric order except for Cr introduction. We discovered that the incorporation of each transition metal imposes a distinct magnetic behavior on the lead iron niobate system; antiferro-, hard ferro-, and soft ferromagnetism for Cr, Co, and Ni, respectively. This indicates that orbital occupancy and interatomic distance play key roles in the determination of magnetic behavior rather than the magnitude of the individual Bohr magneton. Further investigations are planned, such as X-ray absorption spectroscopy, to clarify the origin of magnetic properties in this system.
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EMC Debugging Technique for Image Equipments
Min-jong Song, Jin-sa Kim
J Electr Electron Mater 2022;35(2):143-148.   Published online March 1, 2022
DOI: https://doi.org/10.4313/JKEM.2022.35.2.5
For the purpose of treating health checkups and recovery of patients in a super-aged society, hospitals use devices designed with a reduction circuit of electromagnetic waves associated with the specific absorption rate of electromagnetic waves absorbed by the human body. In this paper, we proposed a filter improvement design method capable of reducing electromagnetic waves. As a result of confirming the validity of the proposed technique through simulation and experimental results, the following result values were obtained. Applying the common-mode (CM) inductor 4 mH to a calibration circuit, noise decreased in a multiband spectrum. Using the differential mode(DM) inductor 40 μH element in the primary calibration circuit, the noise decreased by 15 dB or more in the 3 MHz band spectrum. Also, applying the Admittance Capacitance (Y-Cap) 10 nF element in the secondary calibration circuit resulted in the decrease by more than 30 dB in the band spectrum before 2 MHz. After using a common-mode inductor 4 mH element in the tertiary calibration circuit, it decreased by more than 15 dB in the band spectrum after 2 MHz.
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Effect of Structure Change in Second-Generation Superconducting Wire Stabilization Layer on Resistivity Characteristics
Sang-jae Ban, Ho-ik Du, Hyun-gi Jeong, Seung-gyu Doo, Sung-chae Yang
J Electr Electron Mater 2022;35(2):172-177.   Published online March 1, 2022
DOI: https://doi.org/10.4313/JKEM.2022.35.2.10
The quench voltage of the second-generation superconducting wire is affected by the resistivity characteristics of the stabilization layer. The specific resistance of the stabilization layer can be changed by the deposition process using RF magnetron sputtering. In this paper, a thin film made of a homogeneous material (Ag) and a dissimilar material (Cu) was deposited on the stabilization layer of the second-generation superconducting wire through RF magnetron sputtering. We found that the specific resistance was reduced by increasing the thickness of the stabilization layer. The reduction in the resistivity of the stabilization layer led to a decrease in the quench voltage of the second-generation superconducting wire. We suggest that various characteristic changes of the second-generation superconducting wire can be expected through the successful change in the resistivity of the stabilization layer of the proposed deposition process.
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Structural, Electrical, and Optical Properties of AGZO Thin Films Using RF Magnetron Sputtering System Under Ar Flow Rates
Seok-hyeon Jang, Deok Kyu Kim
J Electr Electron Mater 2022;35(1):32-36.   Published online January 1, 2022
DOI: https://doi.org/10.4313/JKEM.2022.35.1.5
AGZO thin films were deposited on glass substrates using RF magnetron sputtering system under Ar flow rates, and their structural, electrical, and optical properties were analyzed systematically. As a result of the XRD pattern, the peak of the (002) (2θ≈33.7˚) orientation was observed, and it was found to have a hexagonal wurtzite structure. The sheet resistance of Ar 5 sccm was 3.073×102 Ω/sq and showed the best electrical properties because of the improvement of mobility due to the increase of the grain size and the variation of RMS roughness. In addition, the average transmittance was more than 90% for all samples, which demonstrated good optical properties. It is expected that the TCO characteristics can be improved by controlling Ar flow rates, and this will increase the efficiency of photoelectronic devices such as OLED and solar cells.
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Neutron Irradiation Effect of YBa2Cu3O7-y Superconductor
Sang Heon Lee
J Electr Electron Mater 2021;34(6):438-441.   Published online November 1, 2021
DOI: https://doi.org/10.4313/JKEM.2021.34.6.6
The electrical characteristics of single-crystal composite superconductors produced by a melting process were studied by neutron irradiation. In order to improve the current characteristics of the YBa2Cu3O7-y superconductor, it is necessary to form an effective flux pinning center inside the superconductor. In this study, an increase in flux pinning was attempted through neutron irradiation onto YBa2Cu3O7-y superconductors. The neutron irradiation was performed at 30 MeV for 500 sec, The electrical properties of the superconductors were measured in a magnetic field of 5 Tesla at 50 K using a magnetic properties measurement system (MPMS). After neutron irradiation, the critical current density of the YBa2Cu3O7-y superconductor in a 1 Tesla magnetic field was 1×105 A/㎠. Once neutrons were irradiated at 30 MeV and 10 μA for 500 sec, the critical current density was observed to increase significantly. When neutrons are irradiated to a superconductor, micro-defects are created in the superconductor, and they act as flux pinning centers that hold the magnetic field generated when an electric current flows.
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Soft Robots Based on Magnetic Actuator
Gyu-Lyeong Nor, Moon Kee Choi
J Electr Electron Mater 2021;34(6):401-415.   Published online November 1, 2021
DOI: https://doi.org/10.4313/JKEM.2021.34.6.2
Soft robots are promising devices for applications in drug delivery, sensing, and manufacturing. Traditional hard robotics are manufactured with rigid materials and their degrees of motion are constrained by the orientation of the joints. In contrast to rigid counterpart, soft robotics, employing soft and stretchable materials that easily deforms in shape, can realize complex motions (i.e., locomotion, swimming, and grappling) with a simple structure, and easily adapt to dynamic environment. Among them, the magnetic actuators exhibit unique characteristics such as rapid and accurate motion control, biocompatibility, and facile remote controllability, which make them promising candidates for the next-generation soft robots. Especially, the magnetic actuators instantly response to the stimuli, and show no-hysteresis during the recovery process, essential for continuous motion control. Here, we present the state-of-the-art fabrication process of magnetically controllable nano-/micro-composites, magnetically aligning process of the composites, and 1-dimensional/multi-dimensional multimodal motion control for the next-generation soft actuators.
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Characteristics of Magnetoelectric Composite with Rosen Type Piezoelectric Transducer Structure
Sung Hoon Park, Woon-ha Yoon, Deepak Rajaram Patil, Jungho Ryu
J Electr Electron Mater 2021;34(6):480-486.   Published online November 1, 2021
DOI: https://doi.org/10.4313/JKEM.2021.34.6.13
Magnetoelectric (ME) composite is composed of a piezoelectric material and a magnetostrictive material. Among various ME structures, 2-2 type layered ME composites are anticipated to be used as high-sensitivity magnetic field sensors and energy harvesting devices especially operating at its resonance modes. Rosen type piezoelectric transducer using piezoelectric material is known to amplify a small electrical input voltage to a large electrical output voltage. The output voltage of these Rosen type piezoelectric transducers can be further enhanced by modifying them into ME composite structures. Herein, we fabricated Rosen type ME composites by sandwiching Rosen type PMN-PZT single crystal between two Ni layers and studied their ME coupling. However, the voltage step-up ratio at the resonance frequency was found to be smaller than the value calculated with αME value. The ATILA FEA (Finite Elements Analysis) simulation results showed that the position of the nodal point was changed with the presence of a magnetostrictive layer. Thus, while designing a Rosen type ME composite with high performance in a resonant driving situation, it is necessary to optimize the position of the nodal point by optimizing the thickness or length of the magnetostrictive layer.
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Fabrication of Bulk High-Tc Superconductor
Sang Heon Lee
J Electr Electron Mater 2021;34(5):333-336.   Published online September 1, 2021
DOI: https://doi.org/10.4313/JKEM.2021.34.5.9
Oxide YBCO bulk superconductors are manufactured using the melt process. Because seed crystal growth method utilizes a slow-spreading layer-by-layer reaction, a long-term heat treatment is required to manufacture a single-crystal specimen of several cm. In this study, the melt process method was applied to compensate for the shortcomings of the seed crystal growth method. The thickness of the upper and lower pellets of the YBCO bulk was molded to 40 mm, and YBCO superconductor was produced by heat treatment. The measurement results of capture magnetism was in line with the literature. This results in a relationship that the higher the growth of Y211 particle in the YBCO, the higher the superconducting properties. We analyzed the YBCO superconductor, focusing on the Y2BaCuO5 particle distribution.
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Recent Progress in Magneto-Mechano-Electric Generators
Geon-tae Hwang, Jungho Ryu, Woon-ha Yoon
J Electr Electron Mater 2021;34(5):271-282.   Published online September 1, 2021
DOI: https://doi.org/10.4313/JKEM.2021.34.5.2
The internet of things (IoT) technology is a key component for the advent of 4th industrial revolution, which is the network of home appliances, infrastructures, and vehicles to remotely investigate these systems. For the operation of compact IoT devices, batteries are widely used as electric power, and the limited lifetime of batteries inevitably leads to periodic replacement. Magneto-mechano-electric (MME) generators may be alternatives to batteries inside the IoT devices by converting stray magnetic field into electric energy, since we are always surrounded by ambient alternating current (AC) magnetic fields induced from electric power transmission lines everywhere. This article reviews the recent domestic research progress in high-performance MME generators and their application field for IoT and electronic devices.
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Room-Temperature Ferromagnetic Behavior in Ferroelectric BiFeO3-BaTiO3 System Through Engineered Superexchange Path
Nu-ri Ko, Jae-hyeon Cho, Jongmoon Jang, Wook Jo
J Electr Electron Mater 2021;34(5):386-392.   Published online September 1, 2021
DOI: https://doi.org/10.4313/JKEM.2021.34.5.17
Multiferroics exhibiting the coexistence and a possible coupling of ferromagnetic and ferroelectric order are attracting widespread interest in terms of academic interests and possible applications. However, room-temperature single-phase multiferroics with soft ferromagnetic and displacive ferroelectric properties are still rare owing to the contradiction in the origin of ferromagnetism and ferroelectricity. In this study, we demonstrated that sizable ferromagnetic properties are induced in the ferroelectric bismuth ferrite-barium titanate system simply by introducing Co ions into the A-site. It is noted that all modified compositions exhibit well-saturated magnetic hysteresis loops at room temperature. Especially, 70Bi0.95Co0.05FeO3-30Ba0.95Co0.05TiO3 manifests noticeable ferroelectric and ferromagnetic properties; the spontaneous polarization and the saturation magnetization are 42 μC/㎠ and 3.6 emu/g, respectively. We expect that our methodology will be widely used in the development of perovskite-structured multiferroic oxides.
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Magnetoelectric Polymer Composites
Kyujin Ko, Byung-Il Noh, Su-Chul Yang
J Electr Electron Mater 2021;34(4):229-241.   Published online July 1, 2021
DOI: https://doi.org/10.4313/JKEM.2021.34.4.2
Since 2010, polymer-based magnetoelectric (ME) composites have been developed with detailed investigations of multiferroic properties such as piezoelectric, magnetostrictive, and magnetoelectric, etc. In particular, as a piezoelectric polymer, poly(vinylidene fluoride) and its co-polymers have been widely used in ME composites for energy harvesting, health monitoring, environment treatment, and bio-medical applications. In this study, main research trend and selected experimental results of polymer-based ME composites are briefly reviewed with respect to composite structure as well as application field. A conclusion was drawn that the polymer-based ME composites would be feasible as flexible devices or functional membranes in the near future.
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A Brief Review on Magnetoelectric Multiferroic Oxides
Jae-hyeon Cho, Wook Jo
J Electr Electron Mater 2021;34(3):149-166.   Published online May 1, 2021
DOI: https://doi.org/10.4313/JKEM.2021.34.3.1
Magnetoelectric multiferroics, where a ferromagnetic and a ferroelectric order coexist and are coupled in a single phase, have been a hot topic in condensed matter physics for a long time owing to their ability to facilitate nextgeneration applications. In this review, we briefly introduce basic concept of the magnetoelectric multiferroic oxides as well as their history, physical origins, and significant achievements. The key moments contributing to the progress of magnetoelectric multiferroics are snapshotted chronologically, and then a discussion on the major magnetic exchange interactions and the ferroelectric origins are presented along with their coupling behavior. Furthermore, we argue a need for modifying the present classification of magnetoelectric multiferroics before presenting the evolution of multiferroics using representative examples with their properties such as magnetic/ferroelectric transition temperature, magnetization/electric polarization, and magnetoelectric coefficient. We hope that this brief review will provide the community researchers with insights into magnetoelectric multiferroic oxides.
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In the case of ZnO:Al thin films, it is the best material that can replace ITO that is mainly used as a transparent electrode in electronic devices such as solar cells and flat-panel displays. In this study, ZnO:Al films were fabricated by using the RF dual magnetron sputtering method at various substrate temperatures. As the substrate temperature increased, the crystallinity of the ZnO:Al thin films was improved, and the electrical conductivity and electrical properties of the thin film improved owing to the increase in grain size. In addition, the surface roughness of the ZnO:Al thin films increased due to changes in the surface and density of the thin films. Moreover, the substrate temperature increased the density of thin films and improved their transmittance. To be applied to solar cells and other several electronic devices in the future, the hardness and adhesion properties of the thin film improve as the substrate temperature increases.
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Using facing target magnetron sputtering (FTMS) with a graphite target source, carbon nitride thin films were deposited on silicon and glass substrates at different substrate temperatures to confirm the tribological, electrical, and structural properties of thin films. The substrate temperatures were room temperature, 150℃, and 300℃. The tribology and electrical properties of the carbon nitride thin films were measured as the substrate temperature increased, and a study on the relation between these results and structural properties was conducted. The results show that the increase in the substrate temperature during the fabrication of the carbon nitride thin films increased the hardness and elastic modulus values, the critical load value was increased, and the residual stress value was reduced. Moreover, the increase in the substrate temperature during thin-film deposition was attributed to the improvement in the electrical properties of carbon nitride thin film.
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Properties of ZnO:Ga Thin Films Deposited by RF Magnetron Sputtering with Ar Gas Flows
Deok Kyu Kim
J Electr Electron Mater 2020;33(6):450-453.   Published online November 1, 2020
DOI: https://doi.org/10.4313/JKEM.2021.33.6.4
In this study, ZnO:Ga thin films were fabricated on a glass substrate using various Ar flows by an RF magnetron sputter system at room temperature. The dependencies of Ar flow on different properties were investigated. An appropriate control over the Ar flow led to the formation of a high-quality thin film. The ZnO:Ga films were formed as a hexagonal wurtzite structure with high (002) preferential orientation. The films exhibited a typical columnar microstructure and a smooth top face. The average transmittance was 85~89% within the visible area. By decreasing the Ar flow, the sheet resistance was decreased due to an increase in the grain size and a decrease in the root mean square roughness. The lowest sheet resistance of 86 Ω/□ was obtained at room temperature for the 40 sccm Ar flow.
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