Tae‐Seong Ju

Korea Research Institute of Standards and Science

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i-10 index

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Seungmo Yang

Korea Research Institute of Standards and Science

Kyoung‐Woong Moon

Korea Research Institute of Standards and Science

Chanyong Hwang

Korea Research Institute of Standards and Science

Sungkyun Park

Pusan National University

Changsoo Kim

Korea Research Institute of Standards and Science

Sehwan Song

Pusan National University

Jung‐Il Hong

Daegu Gyeongbuk Institute of Science and Technology

Kab‐Jin Kim

Korea Advanced Institute of Science and Technology

Dooyong Lee

Kyungpook National University

Hee‐Sung Han

Lawrence Berkeley National Laboratory

Cooperative Institutions

Korea Research Institute of Standards and Science

Korea Advanced Institute of Science and Technology

Pusan National University

Government of the Republic of Korea

Yonsei University

Seoul National University

Pohang University of Science and Technology

Korea Basic Science Institute

Daegu Gyeongbuk Institute of Science and Technology

Hanyang University

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Deposition-environment-dependent structural and magnetic property modification of [111]-oriented epitaxial CoFe2O4 films

Ceramics International (2020)

Dooyong Lee Tae‐Seong Ju Chang-Woo Cho Jisung Lee Hyegyoung Kim

10.1016/j.ceramint.2020.04.247

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Citations (4)

Perpendicular Magnetic Anisotropy Tilting for Spin-Orbit Torque-Induced Field-Free Switching of Magnetization

Sang Sun Lee Tae‐Seong Ju Kyoung‐Woong Moon Seungmo Yang

Since the discovery of spin-orbit torque, it has garnered significant attention as one of potential spintronics building blocks, owing to its distinct advantages, such as fast switching capabilities. For the practical application of spin-orbit torque, several technical challenges remain; a primary one being the elimination of the necessity for an external magnetic field during switching process. To address this issue, here, we thoroughly explore the nature of perpendicular magnetic anisotropy tilting via wedge sputtering deposition incorporating a physical barrier. We precisely quantify the tilted angle of magnetic anisotropy, and introduce a way to determine the direction of the magnetic anisotropy tilting. In addition, the realization of field-free magnetization switching using the tilted perpendicular magnetic anisotropy is experimentally demonstrated, ensuring the controllability of polarity of the switching.

Orbit (dynamics)

10.2139/ssrn.4604053

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Magnetic Skyrmion Transistor Gated with Voltage‐Controlled Magnetic Anisotropy

Advanced Materials (2022)

Seungmo Yang Jong Wan Son Tae‐Seong Ju Minh Duc Tran Hee‐Sung Han

Abstract The paradigm shift of information carriers from charge to spin has long been awaited in modern electronics. The invention of the spin‐information transistor is expected to be an essential building block for the future development of spintronics. Here, a proof‐of‐concept experiment of a magnetic skyrmion transistor working at room temperature, which has never been demonstrated experimentally, is introduced. With the spatially uniform control of magnetic anisotropy, the shape and topology of a skyrmion when passing the controlled area can be maintained. The findings will open a new route toward the design and realization of skyrmion‐based spintronic devices in the near future.

Skyrmion

10.1002/adma.202208881

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Citations (20)

Atomic scale interface engineering for realizing a perpendicularly magnetized CoFeB-based skyrmion hosting material

Applied Physics Letters (2023)

Sang Sun Lee Tae‐Seong Ju Hee‐Sung Han Mi‐Young Im Changsoo Kim

Néel-type magnetic skyrmions in perpendicularly magnetized systems have attracted considerable interest due to their potential in fundamental research on topological objects and spintronics applications. Various systems have been explored to study Néel-type magnetic skyrmions, including repeated magnetic multilayers, two-dimensional materials, and single magnetic thin-films. Among these, single magnetic thin-films, especially a CoFeB single layer, offers multiple benefits, such as reduced defect energy, high mobility, and easy integration with existing magnetoresistive random access memory technology. However, optimizing CoFeB-based skyrmion hosting materials remains challenging and requires further systematic and comprehensive investigation. In this study, we examine the effect of atomic-scale interface engineering by inserting a Ta layer between the CoFeB/MgO interface on perpendicular magnetic anisotropy, saturation magnetization, and Dzyaloshinskii–Moriya interaction. Moreover, we provide a guideline for engineering material parameters and demonstrate the validity of atomic-scale interface engineering. Our findings contribute to the development of optimized CoFeB-based skyrmion hosting materials.

Skyrmion

Atomic units

Interface (matter)

10.1063/5.0153777

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Citations (1)

Field‐Free Switching of Magnetization by Tilting the Perpendicular Magnetic Anisotropy of Gd/Co Multilayers

Advanced Functional Materials (2022)

Hyun‐Joong Kim Kyoung‐Woong Moon Bao Xuan Tran Seongsoo Yoon Changsoo Kim

Abstract Efficient current‐induced switching of perpendicular magnetization is an essential task in spintronics for realizing high‐performance information processing and for storage device application. However, the spin‐orbit torque (SOT) by injection of in‐plane polarized spins cannot deterministically switch the magnetization of ferromagnetic thin films with perpendicular magnetic anisotropy (PMA) without an additionally applied in‐plane external magnetic field to break the symmetry of the PMA. Considering the difficulties of applying the magnetic field to the localized area only within a device structure, it is essential to contrive a facile field‐free SOT switching mechanism. Here, deterministic field‐free SOT switching of perpendicular magnetization is achieved in amorphous and ferrimagnetic Gd/Co multilayers accompanied by a tilted magnetic anisotropy axis. This tilted anisotropy originates from the combined contributions of many internal anisotropies in different orientations from the multilayers and is shown to be controllable. It is expected that the introduction of controlled tilted anisotropy into Gd/Co multilayers over the entire film surface in the present study can be extended to the development of wafer‐scale technologies for the spintronics memory and logic devices.

Ferrimagnetism

10.1002/adfm.202112561

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Citations (28)

Correlation between Symmetry and Phase Transition Temperature of VO₂ Films Deposited on Al₂O₃ Substrates with Various Orientations

Advanced Electronic Materials (2021)

Yesul Choi Dooyong Lee Sehwan Song Jiwoong Kim Tae‐Seong Ju

Abstract The structural aspects of the insulator–metal transition (IMT) characteristics of VO 2 are sensitive to the octahedral symmetry variation of VO 6 . By varying substrate orientation ( c ‐, a ‐, and m ‐plane Al 2 O 3 ), the correlation between IMT temperature and local symmetry is investigated. For a VO 2 film deposited on m ‐plane Al 2 O 3 , which has high symmetry due to fewer domain boundaries induced by m ‐plane Al 2 O 3 , the IMT temperature is low (326.47 K). In contrast, for a film deposited on c ‐plane Al 2 O 3 (having lower symmetry), the IMT temperature is the highest (336.74 K) among the films used in this work. Furthermore, temperature‐dependent Raman spectra reveals that the structural phase transition temperature decreases in the order of the VO 2 film deposited on c ‐, a ‐, and m ‐plane Al 2 O 3 , suggesting that the symmetrical structure reduces the activation energy for IMT by decreasing thermodynamic energy. These results demonstrate that structural symmetry plays a crucial role in lowering the transition temperature.

10.1002/aelm.202000874

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Citations (16)

Programmable Racetrack for Magnetic Domain Wall Motion via Local Tuning of Exchange Biased Field

Advanced Electronic Materials (2024)

Hyun‐Joong Kim Kyoung‐Woong Moon Seongsoo Yoon Kyongmo An Changsoo Kim

Abstract To overcome memory bottleneck issues in memory‐centric chip technologies, in‐memory computing has been considered an alternative route involving simultaneous data storage and computing in a memory network. In the context of spintronics, a memory‐in‐logic device based on spin‐transfer‐torque or spin‐orbit‐torque magnetoresistive random‐access memory, and a magnetic domain wall (DW) racetrack has been studied. To expand the functionalities of a conventional magnetic DW racetrack, the study devises a reprogrammable exchange‐biased DW racetrack with local engineering of the exchange bias field ( H E ) in continuous magnetic films without requiring a lithography process for specific patterning of the films. Furthermore, current‐driven and field‐driven DW motion along the exchange‐biased racetrack is demonstrated. Additionally, within the route of the locally different exchange‐biased racetrack, a gate function can be performed to guide or stop DW motion by locally tuning H E . The complex maze racetrack is rewritable, and multiple input channels can be controlled.

Racetrack memory

Magnetoresistive random-access memory

Domain wall (magnetism)

Exchange bias

Spin-transfer torque

Non-Volatile Memory

10.1002/aelm.202400027

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Citations (1)

Universal Hopping Motion Protected by Structural Topology (Adv. Mater. 40/2022)

Advanced Materials (2022)

Moojune Song Mujin You Seungmo Yang Tae‐Seong Ju Kyoung‐Woong Moon

Skyrmion Motion Understanding skyrmion motion is essential for the efficient operation of skyrmionic devices. In article number 2203275, Chanyong Hwang, Kyoung-Whan Kim, Albert Min Gyu Park, Kab-Jin Kim, and co-workers uncover a universal scaling behavior in the current-driven motion of skyrmions. The topology of the shape of the interface drags the skyrmions and causes them to show hopping properties distinct from the creep motion expected for magnetic domains. The universal scaling can provide insights for implementing skyrmion devices and understanding the dynamics of moving bodies with a closed interface.

Skyrmion

10.1002/adma.202270277

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Citations (0)

Universality of stripe domain width change by an in-plane magnetic field

Journal of Magnetism and Magnetic Materials (2021)

Seungmo Yang Kyoung‐Woong Moon Tae‐Seong Ju Changsoo Kim Sungkyun Park

Single domain

10.1016/j.jmmm.2021.168381

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Citations (13)

Universal method for magnetic skyrmion bubble generation by controlling the stripe domain instability

NPG Asia Materials (2021)

Kyoung‐Woong Moon Seungmo Yang Tae‐Seong Ju Changsoo Kim Byoung Sun Chun

Abstract Magnetic skyrmions, which are topological swirling spin textures, have drawn much attention in spintronics because of their use as an information carrier with distinct robustness rooted in their topological nature. Real-time generation of skyrmions is therefore imperative for realizing skyrmion-based spintronic devices. However, to date, experimental demonstration has been limited to exquisite works with well-tuned samples. Here, we report a method to generate skyrmions by driving the stripe instability via an in-plane magnetic field. We have demonstrated that the key parameter determining the stripe domain instability is the stripe width, regardless of other material parameters. This skyrmion generation method can be applicable to generic magnetic films with perpendicular magnetic anisotropy. Our work will facilitate the development of skyrmion-based devices by offering a general method for controlling a large skyrmion population.

Skyrmion

Robustness

Domain wall (magnetism)

10.1038/s41427-021-00290-3

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Citations (18)