1
|
Ji Y, Yang S, Ahn HB, Moon KW, Ju TS, Im MY, Han HS, Lee J, Park SY, Lee C, Kim KJ, Hwang C. Direct Observation of Room-Temperature Magnetic Skyrmion Motion Driven by Ultra-Low Current Density in Van Der Waals Ferromagnets. Adv Mater 2024:e2312013. [PMID: 38270245 DOI: 10.1002/adma.202312013] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/12/2023] [Revised: 01/05/2024] [Indexed: 01/26/2024]
Abstract
The recent discovery of room-temperature ferromagnetism in 2D van der Waals (vdW) materials, such as Fe3 GaTe2 (FGaT), has garnered significant interest in offering a robust platform for 2D spintronic applications. Various fundamental operations essential for the realization of 2D spintronics devices are experimentally confirmed using these materials at room temperature, such as current-induced magnetization switching or tunneling magnetoresistance. Nevertheless, the potential applications of magnetic skyrmions in FGaT systems at room temperature remain unexplored. In this work, the current-induced generation of magnetic skyrmions in FGaT flakes employing high-resolution magnetic transmission soft X-ray microscopy is introduced, supported by a feasible mechanism based on thermal effects. Furthermore, direct observation of the current-induced magnetic skyrmion motion at room temperature in FGaT flakes is presented with ultra-low threshold current density. This work highlights the potential of FGaT as a foundation for room-temperature-operating 2D skyrmion device applications.
Collapse
Affiliation(s)
- Yubin Ji
- Department of Physics, Korea Advanced Institute of Science and Technology, Daejeon, 34141, Republic of Korea
| | - Seungmo Yang
- Quantum Spin Team, Korea Research Institute of Standards and Science, Daejeon, 34113, Republic of Korea
| | - Hyo-Bin Ahn
- SKKU Advanced Institute of Nanotechnology, Sungkyunkwan University, Suwon, 16419, Republic of Korea
| | - Kyoung-Woong Moon
- Quantum Spin Team, Korea Research Institute of Standards and Science, Daejeon, 34113, Republic of Korea
| | - Tae-Seong Ju
- Quantum Spin Team, Korea Research Institute of Standards and Science, Daejeon, 34113, Republic of Korea
| | - Mi-Young Im
- Center for X-ray Optics, Lawrence Berkeley National Laboratory, Berkeley, CA, 94720, USA
| | - Hee-Sung Han
- Center for X-ray Optics, Lawrence Berkeley National Laboratory, Berkeley, CA, 94720, USA
- Department of Materials Science and Engineering, Korea National University of Transportation, Chungju, 27469, Republic of Korea
| | - Jisung Lee
- Center for scientific instrumentation, Korea Basic Science Institute, Daejeon, 34133, Republic of Korea
| | - Seung-Young Park
- Center for scientific instrumentation, Korea Basic Science Institute, Daejeon, 34133, Republic of Korea
| | - Changgu Lee
- School of Mechanical Engineering, Sungykunkwan University, Suwon, 16419, Republic of Korea
| | - Kab-Jin Kim
- Department of Physics, Korea Advanced Institute of Science and Technology, Daejeon, 34141, Republic of Korea
| | - Chanyong Hwang
- Quantum Spin Team, Korea Research Institute of Standards and Science, Daejeon, 34113, Republic of Korea
| |
Collapse
|
2
|
Son JW, Yang S, Ju TS, Hwang C, Moon KW. Measurement of spin-orbit torque using field counterbalancing in radial current geometry. Sci Rep 2023; 13:19357. [PMID: 37938612 PMCID: PMC10632434 DOI: 10.1038/s41598-023-46658-z] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/08/2023] [Accepted: 11/03/2023] [Indexed: 11/09/2023] Open
Abstract
Controlling the direction of magnetization with an electric current, rather than a magnetic field, is a powerful technique in spintronics. Spin-orbit torque, which generates an effective magnetic field from the injected current, is a promising method for this purpose. Here we show an approach for quantifying the magnitude of spin-orbit torque from a single magnetic image. To achieve this, we deposited two concentric electrodes on top of the magnetic sample to flow a radial current. By counterbalancing the current effect with an external magnetic field, we can create a stable circular magnetization state. We measure the magnitude of spin-orbit torque from the stable radius, providing a new tool for characterizing spin-orbit torque.
Collapse
Affiliation(s)
- Jong Wan Son
- Quantum Spin Team, Korea Research Institute of Standards and Science, Daejeon, 34113, Republic of Korea
| | - Seungmo Yang
- Quantum Spin Team, Korea Research Institute of Standards and Science, Daejeon, 34113, Republic of Korea
| | - Tae-Seong Ju
- Quantum Spin Team, Korea Research Institute of Standards and Science, Daejeon, 34113, Republic of Korea
| | - Chanyong Hwang
- Quantum Spin Team, Korea Research Institute of Standards and Science, Daejeon, 34113, Republic of Korea.
| | - Kyoung-Woong Moon
- Quantum Spin Team, Korea Research Institute of Standards and Science, Daejeon, 34113, Republic of Korea.
| |
Collapse
|
3
|
Yang S, Son JW, Ju TS, Tran DM, Han HS, Park S, Park BH, Moon KW, Hwang C. Magnetic Skyrmion Transistor Gated with Voltage-Controlled Magnetic Anisotropy. Adv Mater 2023; 35:e2208881. [PMID: 36511234 DOI: 10.1002/adma.202208881] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/27/2022] [Revised: 11/27/2022] [Indexed: 06/17/2023]
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.
Collapse
Affiliation(s)
- Seungmo Yang
- Quantum Spin Team, Korea Research Institute of Standards and Science, Daejeon, 34113, Republic of Korea
| | - Jong Wan Son
- Quantum Spin Team, Korea Research Institute of Standards and Science, Daejeon, 34113, Republic of Korea
| | - Tae-Seong Ju
- Quantum Spin Team, Korea Research Institute of Standards and Science, Daejeon, 34113, Republic of Korea
- Department of Physics, Pusan National University, Busan, 46241, Republic of Korea
| | - Duc Minh Tran
- Division of Quantum Phases and Devices, Department of Physics, Konkuk University, Seoul, 05029, Republic of Korea
| | - Hee-Sung Han
- Department of Materials Science and Engineering, Ulsan National Institute of Science and Technology (UNIST), Ulsan, 44919, Republic of Korea
| | - Sungkyun Park
- Department of Physics, Pusan National University, Busan, 46241, Republic of Korea
| | - Bae Ho Park
- Division of Quantum Phases and Devices, Department of Physics, Konkuk University, Seoul, 05029, Republic of Korea
| | - Kyoung-Woong Moon
- Quantum Spin Team, Korea Research Institute of Standards and Science, Daejeon, 34113, Republic of Korea
| | - Chanyong Hwang
- Quantum Spin Team, Korea Research Institute of Standards and Science, Daejeon, 34113, Republic of Korea
| |
Collapse
|
4
|
Yang S, Ju TS, Kim C, Kim HJ, An K, Moon KW, Park S, Hwang C. Magnetic Field Magnitudes Needed for Skyrmion Generation in a General Perpendicularly Magnetized Film. Nano Lett 2022; 22:8430-8436. [PMID: 36282733 PMCID: PMC9650724 DOI: 10.1021/acs.nanolett.2c02268] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 06/06/2022] [Revised: 10/08/2022] [Indexed: 06/16/2023]
Abstract
Due to its topological protection, the magnetic skyrmion has been intensively studied for both fundamental aspects and spintronics applications. However, despite recent advancements in skyrmion research, the deterministic creation of isolated skyrmions in a generic perpendicularly magnetized film is still one of the most essential and challenging techniques. Here, we present a method to create magnetic skyrmions in typical perpendicular magnetic anisotropy (PMA) films by applying a magnetic field pulse and a method to determine the magnitude of the required external magnetic fields. Furthermore, to demonstrate the usefulness of this result for future skyrmion research, we also experimentally study the PMA dependence on the minimum size of skyrmions. Although field-driven skyrmion generation is unsuitable for device application, this result can provide an easier approach for obtaining isolated skyrmions, making skyrmion-based research more accessible.
Collapse
Affiliation(s)
- Seungmo Yang
- Quantum
Spin Team, Korea Research Institute of Standards
and Science, Daejeon34113, Republic of Korea
| | - Tae-Seong Ju
- Quantum
Spin Team, Korea Research Institute of Standards
and Science, Daejeon34113, Republic of Korea
- Department
of Physics, Pusan National University, Busan46241, Republic of Korea
| | - Changsoo Kim
- Quantum
Spin Team, Korea Research Institute of Standards
and Science, Daejeon34113, Republic of Korea
| | - Hyun-Joong Kim
- Quantum
Spin Team, Korea Research Institute of Standards
and Science, Daejeon34113, Republic of Korea
| | - Kyongmo An
- Quantum
Spin Team, Korea Research Institute of Standards
and Science, Daejeon34113, Republic of Korea
| | - Kyoung-Woong Moon
- Quantum
Spin Team, Korea Research Institute of Standards
and Science, Daejeon34113, Republic of Korea
| | - Sungkyun Park
- Department
of Physics, Pusan National University, Busan46241, Republic of Korea
| | - Chanyong Hwang
- Quantum
Spin Team, Korea Research Institute of Standards
and Science, Daejeon34113, Republic of Korea
| |
Collapse
|
5
|
Song M, You M, Yang S, Ju TS, Moon KW, Hwang C, Kim KW, Park AMG, Kim KJ. Universal Hopping Motion Protected by Structural Topology. Adv Mater 2022; 34:e2203275. [PMID: 35985670 DOI: 10.1002/adma.202203275] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/11/2022] [Revised: 07/28/2022] [Indexed: 06/15/2023]
Abstract
A scaling law elucidates the universality in nature, presiding over many physical phenomena which seem unrelated. Thus, exploring the universality class of scaling law in a particular system enlightens its physical nature in relevance to other systems and sometimes unearths an unprecedented new dynamic phase. Here, the dynamics of weakly driven magnetic skyrmions are investigated, and its scaling law is compared with the motion of a magnetic domain wall (DW) creep. This study finds that the skyrmion does not follow the scaling law of the DW creep in 2D space but instead shows a hopping behavior similar to that of the particle-like DW in 1D confinement. In addition, the hopping law satisfies even when a topological charge of the skyrmion is removed. Therefore, the distinct scaling behavior between the magnetic skyrmion and the DW stems from a general principle beyond the topological charge. This study demonstrates that the hopping behavior of skyrmions originates from the bottleneck process induced by DW segments with diverging collective lengths, which is inevitable in any closed-shape spin structure in 2D. This work reveals that the structural topology of magnetic texture determines the universality class of its weakly driven motion, which is distinguished from the universality class of magnetic DW creep.
Collapse
Affiliation(s)
- Moojune Song
- Department of Physics, Korea Advanced Institute of Science and Technology, Daejeon, 34141, Republic of Korea
| | - Mujin You
- Department of Physics, Korea Advanced Institute of Science and Technology, Daejeon, 34141, Republic of Korea
| | - Seungmo Yang
- Quantum Spin Team, Korea Research Institute of Standards and Science, Daejeon, 34113, Republic of Korea
| | - Tae-Seong Ju
- Quantum Spin Team, Korea Research Institute of Standards and Science, Daejeon, 34113, Republic of Korea
| | - Kyoung-Woong Moon
- Quantum Spin Team, Korea Research Institute of Standards and Science, Daejeon, 34113, Republic of Korea
| | - Chanyong Hwang
- Quantum Spin Team, Korea Research Institute of Standards and Science, Daejeon, 34113, Republic of Korea
| | - Kyoung-Whan Kim
- Center for Spintronics, Korea Institute of Science and Technology, Seoul, 02792, Republic of Korea
| | - Albert Min Gyu Park
- Department of Physics, Korea Advanced Institute of Science and Technology, Daejeon, 34141, Republic of Korea
| | - Kab-Jin Kim
- Department of Physics, Korea Advanced Institute of Science and Technology, Daejeon, 34141, Republic of Korea
| |
Collapse
|
6
|
Yang S, Moon KW, Ju TS, Kim C, Kim HJ, Kim J, Tran BX, Hong JI, Hwang C. Electrical Generation and Deletion of Magnetic Skyrmion-Bubbles via Vertical Current Injection. Adv Mater 2021; 33:e2104406. [PMID: 34569658 DOI: 10.1002/adma.202104406] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/09/2021] [Revised: 08/28/2021] [Indexed: 06/13/2023]
Abstract
The magnetic skyrmion is a topologically protected spin texture that has attracted much attention as a promising information carrier because of its distinct features of suitability for high-density storage, low power consumption, and stability. One of the skyrmion devices proposed so far is the skyrmion racetrack memory, which is the skyrmion version of the domain-wall racetrack memory. For application in devices, skyrmion racetrack memory requires electrical generation, deletion, and displacement of isolated skyrmions. Despite the progress in experimental demonstrations of skyrmion generation, deletion, and displacement, these three operations have yet to be realized in one device. Here, a route for generating and deleting isolated skyrmion-bubbles through vertical current injection with an explanation of its microscopic origin is presented. By combining the proposed skyrmion-bubble generation/deletion method with the spin-orbit-torque-driven skyrmion shift, a proof-of-concept experimental demonstration of the skyrmion racetrack memory operation in a three-terminal device structure is provided.
Collapse
Affiliation(s)
- Seungmo Yang
- Quantum Spin Team, Korea Research Institute of Standards and Science, Daejeon, 34113, Republic of Korea
| | - Kyoung-Woong Moon
- Quantum Spin Team, Korea Research Institute of Standards and Science, Daejeon, 34113, Republic of Korea
| | - Tae-Seong Ju
- Quantum Spin Team, Korea Research Institute of Standards and Science, Daejeon, 34113, Republic of Korea
| | - Changsoo Kim
- Quantum Spin Team, Korea Research Institute of Standards and Science, Daejeon, 34113, Republic of Korea
| | - Hyun-Joong Kim
- Quantum Spin Team, Korea Research Institute of Standards and Science, Daejeon, 34113, Republic of Korea
| | - Juran Kim
- Quantum Spin Team, Korea Research Institute of Standards and Science, Daejeon, 34113, Republic of Korea
| | - Bao Xuan Tran
- Department of Emerging Materials Science, DGIST, Daegu, 42988, Republic of Korea
| | - Jung-Il Hong
- Department of Emerging Materials Science, DGIST, Daegu, 42988, Republic of Korea
| | - Chanyong Hwang
- Quantum Spin Team, Korea Research Institute of Standards and Science, Daejeon, 34113, Republic of Korea
| |
Collapse
|
7
|
Moon KW, Yang S, Hwang C. Reversible magnetic spiral domain. Sci Rep 2021; 11:20970. [PMID: 34697314 PMCID: PMC8546083 DOI: 10.1038/s41598-021-00016-z] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/28/2021] [Accepted: 09/28/2021] [Indexed: 12/01/2022] Open
Abstract
The various spiral structures that exist in nature inspire humanity because of their morphological beauty, and spiral structures are used in various fields, including architecture, engineering, and art. Spiral structures have their own winding directions, and in most spirals, it is difficult to reverse the predetermined winding direction. Here, we show that a rotating spiral exists in magnetic systems for which the winding direction can be easily reversed. A magnetization vector basically has a spiral motion combining a precessional and a damping motion. The application of these basic mechanics to a system composed of magnetic vectors that are affected by a radial current and the Dzyaloshinskii–Moriya interaction forms the rotating magnetic spiral. The winding direction of the magnetic spiral has its own stability, but the direction can be changed using an external magnetic field. This magnetic spiral has a finite size, and the magnetic domain is destroyed at the edge of the spiral, which can create magnetic skyrmions.
Collapse
Affiliation(s)
- Kyoung-Woong Moon
- Quantum Spin Team, Korea Research Institute of Standards and Science, Daejeon, 34113, Republic of Korea
| | - Seungmo Yang
- Quantum Spin Team, Korea Research Institute of Standards and Science, Daejeon, 34113, Republic of Korea
| | - Chanyong Hwang
- Quantum Spin Team, Korea Research Institute of Standards and Science, Daejeon, 34113, Republic of Korea.
| |
Collapse
|
8
|
Kim JM, Kim DJ, Cheon CY, Moon KW, Kim C, Cao Van P, Jeong JR, Hwang C, Lee KJ, Park BG. Observation of Thermal Spin-Orbit Torque in W/CoFeB/MgO Structures. Nano Lett 2020; 20:7803-7810. [PMID: 33054243 DOI: 10.1021/acs.nanolett.0c01702] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/11/2023]
Abstract
Coupling of spin and heat currents enables the spin Nernst effect, the thermal generation of spin currents in nonmagnets that have strong spin-orbit interaction. Analogous to the spin Hall effect that electrically generates spin currents and associated electrical spin-orbit torques (SOTs), the spin Nernst effect can exert thermal SOTs on an adjacent magnetic layer and control the magnetization direction. Here, the thermal SOT caused by the spin Nernst effect is experimentally demonstrated in W/CoFeB/MgO structures. It is found that an in-plane temperature gradient across the sample generates a magnetic torque and modulates the switching field of the perpendicularly magnetized CoFeB. The W thickness dependence suggests that the torque originates mainly from thermal spin currents induced in W. Moreover, the thermal SOT reduces the critical current for SOT-induced magnetization switching, demonstrating that it can be utilized to control the magnetization in spintronic devices.
Collapse
Affiliation(s)
- Jeong-Mok Kim
- Department of Materials Science and Engineering, KAIST 291 Daehak-ro, Yuseong-gu, Daejeon, 34141, Republic of Korea
| | - Dong-Jun Kim
- Department of Materials Science and Engineering, KAIST 291 Daehak-ro, Yuseong-gu, Daejeon, 34141, Republic of Korea
| | - Cheol-Yeon Cheon
- Department of Materials Science and Engineering, KAIST 291 Daehak-ro, Yuseong-gu, Daejeon, 34141, Republic of Korea
| | - Kyoung-Woong Moon
- Center for Nanometrology, Korea Research Institute of Standards and Science 267 Gajung-ro, Yuseong-gu, Daejeon, Korea, 34113, Republic of Korea
| | - Changsoo Kim
- Center for Nanometrology, Korea Research Institute of Standards and Science 267 Gajung-ro, Yuseong-gu, Daejeon, Korea, 34113, Republic of Korea
| | - Phuoc Cao Van
- Department of Materials Science and Engineering, Graduate School of Energy Science and Technology, Chungnam National University, Daejeon, 34134, Republic of Korea
| | - Jong-Ryul Jeong
- Department of Materials Science and Engineering, Graduate School of Energy Science and Technology, Chungnam National University, Daejeon, 34134, Republic of Korea
| | - Chanyong Hwang
- Center for Nanometrology, Korea Research Institute of Standards and Science 267 Gajung-ro, Yuseong-gu, Daejeon, Korea, 34113, Republic of Korea
| | - Kyung-Jin Lee
- Department of Materials Science and Engineering, Korea University KU-KIST Graduate School of Converging Science and Technology, Korea University 145 Anam-ro, Anam-dong, Seongbuk-gu, Seoul, Korea, 02841, Republic of Korea
- Department of Physics, KAIST 291 Daehak-ro, Yuseong-gu, Daejeon, 34141, Republic of Korea
| | - Byong-Guk Park
- Department of Materials Science and Engineering, KAIST 291 Daehak-ro, Yuseong-gu, Daejeon, 34141, Republic of Korea
| |
Collapse
|
9
|
Kim D, Park S, Lee J, Yoon J, Joo S, Kim T, Min KJ, Park SY, Kim C, Moon KW, Lee C, Hong J, Hwang C. Antiferromagnetic coupling of van der Waals ferromagnetic Fe 3GeTe 2. Nanotechnology 2019; 30:245701. [PMID: 30802888 DOI: 10.1088/1361-6528/ab0a37] [Citation(s) in RCA: 20] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/16/2023]
Abstract
Among two-dimensional (2D) layered van der Waals materials, ferromagnetic 2D materials can be useful for compact low-power spintronic applications. One promising candidate material is Fe3GeTe2 (FGT), which has a strong perpendicular magnetic anisotropy and relatively high Curie temperature. In this study, we confirmed that an oxide layer (O-FGT) naturally forms on top of exfoliated FGT and that an antiferromagnetic coupling (AFC) exists between FGT and O-FGT layers. From a first-principles calculation, oxide formation at the interface of each layer induces an AFC between the layers. An AFC causes a tailed hysteresis loop, where two-magnetization reversal curves are included, and a negative remanence magnetization at a certain temperature range.
Collapse
Affiliation(s)
- Dongseuk Kim
- Quantum Technology Institute, Korea Research Institute of Standards and Science, Daejeon 34113, Republic of Korea
| | | | | | | | | | | | | | | | | | | | | | | | | |
Collapse
|
10
|
Moon KW, Kim C, Yoon J, Choi JW, Kim DO, Song KM, Kim D, Chun BS, Hwang C. A spin torque meter with magnetic facet domains. Nat Commun 2018; 9:3788. [PMID: 30224700 PMCID: PMC6141574 DOI: 10.1038/s41467-018-06223-z] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/24/2017] [Accepted: 08/24/2018] [Indexed: 11/23/2022] Open
Abstract
Current-induced magnetic domain wall (DW) motion is an important operating principle of spintronic devices. Injected current generates spin torques (STs) on the DWs in two ways. One is the spin transfer from magnetic domains to the walls by the current flowing in the magnet. Current flow in attached heavy metals also generates another ST because of the spin-Hall effect. Both phenomena explain the wall motions well; therefore, their respective contribution is an important issue. Here, we show the simultaneous measurement of both torques by using magnetic facet domains that form mountain-shaped domains with straight walls. When the STs and the external magnetic field push the walls in opposite directions, the walls should have equilibrium angles to create balanced states. Such angles can be modulated by an additional in-plane magnetic field. Angle measurements distinguish the STs because each torque has a distinct mechanism related to the DW structure.
Collapse
Affiliation(s)
- Kyoung-Woong Moon
- Spin Convergence Research Team, Korea Research Institute of Standards and Science, Daejeon, 34113, Republic of Korea
| | - Changsoo Kim
- Spin Convergence Research Team, Korea Research Institute of Standards and Science, Daejeon, 34113, Republic of Korea
| | - Jungbum Yoon
- Spin Convergence Research Team, Korea Research Institute of Standards and Science, Daejeon, 34113, Republic of Korea
| | - Jun Woo Choi
- Center for Spintronics, Korea Institute of Science and Technology, Seoul, 02792, Republic of Korea
| | - Dong-Ok Kim
- Center for Spintronics, Korea Institute of Science and Technology, Seoul, 02792, Republic of Korea
- Department of Physics, Soongsil University, Seoul, 06978, Republic of Korea
| | - Kyung Mee Song
- Center for Spintronics, Korea Institute of Science and Technology, Seoul, 02792, Republic of Korea
- Department of Physics, Sookmyung Women's University, Seoul, 04130, Republic of Korea
| | - Dongseuk Kim
- Spin Convergence Research Team, Korea Research Institute of Standards and Science, Daejeon, 34113, Republic of Korea
| | - Byong Sun Chun
- Spin Convergence Research Team, Korea Research Institute of Standards and Science, Daejeon, 34113, Republic of Korea
| | - Chanyong Hwang
- Spin Convergence Research Team, Korea Research Institute of Standards and Science, Daejeon, 34113, Republic of Korea.
| |
Collapse
|
11
|
Choi SW, Kim MK, Han SW, Han SH, Lee BK, Lee SU, Hur SH, Lim SW, Moon KW, Lee SG, Lee SH, Oh SK, Chea JG, Joo SJ, Jo MC, Hong KS, Ryu KH. Apparent treatment-resistant hypertension among elderly Korean hypertensives: an insight from the HIT registry. J Hum Hypertens 2013; 28:201-5. [PMID: 23985877 DOI: 10.1038/jhh.2013.76] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/04/2013] [Revised: 07/09/2013] [Accepted: 07/10/2013] [Indexed: 11/09/2022]
Abstract
The aim of this study was to determine the clinical characteristics of patients with resistant hypertension (RH) and predictors among elderly Korean hypertensives. This prospective, multi-center, observational study evaluated 2439 elderly hypertensive patients between December 2008 and November 2011, who visited secondary hypertension clinics for high blood pressure (BP). Patients were categorized as resistant if their BP was ≥140/90 mm Hg and if they reported using antihypertensive medications from three different drug classes, including a diuretic or drugs from ≥4 antihypertensive drug classes, regardless of BP. Characteristics of patients with RH were compared with those of patients who were controlled with one or two antihypertensive medications after 6-month antihypertensive treatment. In comparison with 837 patients with non-RH, 404 patients with RH were more likely to be aware of their status of high BP before enrollment and have a high baseline systolic BP ≥160 mm Hg, microalbuminuria, high body mass index (BMI) ≥24 kg m(-2) and diabetes mellitus (DM). In drug-naive patients, awareness of hypertension at baseline was the only independent predictor for RH. In elderly Korean hypertensives, BMI (≥24 kg m(-2)), baseline systolic BP (≥160 mm Hg), microalbuminuria, DM and awareness of hypertension showed an association with RH.
Collapse
Affiliation(s)
- S-W Choi
- Division of Cardiology, Dongtan Sacred Heart Hospital, Hallym University, Hwaseong, Korea
| | - M-K Kim
- Division of Cardiology, Dongtan Sacred Heart Hospital, Hallym University, Hwaseong, Korea
| | - S W Han
- Department of Internal Medicine, Hangang Sacred Heart Hospital, Hallym University, Seoul, Korea
| | - S H Han
- Division of Cardiology, Gachon University Gil Hospital, Incheon, Korea
| | - B K Lee
- Division of Cardiology, Gangnam Severance Hospital, Yonsei University, Seoul, Korea
| | - S U Lee
- Department of Internal Medicine, Gwangju Christian Hospital, Gwangju, Korea
| | - S-H Hur
- Division of Cardiology, Daejeon St. Mary's Hospital, The Catholic University of Korea, Daejeon, Korea
| | - S W Lim
- Division of Cardiology, Bundang Cha Hospital, Cha University, Seongnam, Korea
| | - K W Moon
- Division of Cardiology, St. Vincent's Hospital, The Catholic University of Korea, Suwon, Korea
| | - S G Lee
- Division of Cardiology, Ulsan University Hospital, Ulsan, Korea
| | - S H Lee
- Department of Internal Medicine, Dongkang Medical Center, Ulsan, Korea
| | - S K Oh
- Division of Cardiology, Wonkwang University School of Medicine and Hospital, Iksan, Korea
| | - J G Chea
- Division of Cardiology, Chonbuk National University Hospital, Jeonju, Korea
| | - S J Joo
- Division of Cardiology, Jeju National University Hospital, Jeju, Korea
| | - M C Jo
- Division of Cardiology, Chungbuk National University Hospital, Cheongju, Korea
| | - K-S Hong
- Division of Cardiology, Chooncheon Sacred Heart Hospital, Hallym University, Chooncheon, Korea
| | - K-H Ryu
- Division of Cardiology, Dongtan Sacred Heart Hospital, Hallym University, Hwaseong, Korea
| | | |
Collapse
|
12
|
Abstract
We investigate a control scheme for enhancing the controllability of domain-wall (DW) pinning on ferromagnetic devices using an interaction between magnetic charges distributed on a nanobar and at a notch, respectively. The scheme is realized at an artificial notch with a nanobar vertical to it on Permalloy nanowires with an asymmetrical pad. Injection fields for injecting the DWs from the asymmetrical pad to the nanowire show an asymmetrical dependence on the saturation angle for initializing the magnetization of the nanowire, and the injected DWs are pinned by the notch with the nanobar vertical to it. We have found that the landscape of the pinning potential energy experienced by the DWs depends on the magnetized direction of the nanobar and that its level is shifted by the injection field, leading to an increase or decrease in the depinning field with respect to the saturation angle. This is consistent with our estimation based on micromagnetic simulation.
Collapse
Affiliation(s)
- Sung-Min Ahn
- Department of Physics, Seoul National University, Seoul 151-742, Republic of Korea.
| | | |
Collapse
|
13
|
Moon KW, Kim DH, Yoo SC, Cho CG, Hwang S, Kahng B, Min BC, Shin KH, Choe SB. Distinct universality classes of domain wall roughness in two-dimensional Pt/Co/Pt films. Phys Rev Lett 2013; 110:107203. [PMID: 23521290 DOI: 10.1103/physrevlett.110.107203] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/01/2012] [Indexed: 06/01/2023]
Abstract
We demonstrate here that the current-driven domain wall (DW) in two dimensions forms a "facet" roughness, distinctive to the conventional self-affine roughness induced by a magnetic field. Despite the different universality classes of these roughnesses, both the current- and field-driven DW speed follow the same creep law only with opposite angular dependences. Such angular dependences result in a stable facet angle, from which a single DW image can unambiguously quantify the spin-transfer torque efficiency, an essential parameter in DW-mediated nanodevices.
Collapse
Affiliation(s)
- Kyoung-Woong Moon
- CSO and Department of Physics, Seoul National University, Seoul 151-742, Republic of Korea
| | | | | | | | | | | | | | | | | |
Collapse
|
14
|
Lee JC, Kim KJ, Ryu J, Moon KW, Yun SJ, Gim GH, Lee KS, Shin KH, Lee HW, Choe SB. Universality classes of magnetic domain wall motion. Phys Rev Lett 2011; 107:067201. [PMID: 21902363 DOI: 10.1103/physrevlett.107.067201] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/06/2011] [Indexed: 05/31/2023]
Abstract
We examine magnetic domain wall motion in metallic nanowires Pt-Co-Pt. Regardless of whether the motion is driven by either magnetic fields or current, all experimental data fall onto a single universal curve in the creep regime, implying that both the motions belong to the same universality class. This result is in contrast to the report on magnetic semiconductor (Ga,Mn)As exhibiting two different universality classes. Our finding signals the possible existence of yet other universality classes which go beyond the present understanding of the statistical mechanics of driven interfaces.
Collapse
Affiliation(s)
- Jae-Chul Lee
- CSO, Seoul National University, Republic of Korea
| | | | | | | | | | | | | | | | | | | |
Collapse
|
15
|
Ahn SM, Moon KW, Choe SB. Oscillatory reduction of domain wall depinning field by transverse magnetic field in ferromagnetic permalloy nanowires. J Nanosci Nanotechnol 2011; 11:6472-6475. [PMID: 22121738 DOI: 10.1166/jnn.2011.4477] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/31/2023]
Abstract
Reported herein is a possible way of controlling the depinning field of magnetic domain walls (DWs) by using a magnetic field H(T) transverse to the nanowire. A typical notch structure-in the form of triangles on both edges of ferromagnetic Permalloy nanowires-is employed to pin the DWs. The depinning field of the DW initially pinned at the notch is then measured with respect to H(T). Interestingly, it is experimentally found that the depinning field is drastically decreased to almost 0 with increasing H(T), due to the internal shift of the DW position at the notch. Moreover, it is experimentally observed that an oscillatory behavior of the depinning field occurs with respect to H(T), Micromagnetic calculation is performed to model the depinning behavior of the DW pinned at the notch structure with respect to H(T). It is ascribed to the natural edge roughness of the nanowire, which means the edge roughness plays an important role in determination of the depinning field.
Collapse
Affiliation(s)
- Sung-Min Ahn
- Department of Physics, Seoul National University, Seoul, 151-747, Republic of Korea
| | | | | |
Collapse
|
16
|
Ahn SM, Moon KW, Cho CG, Choe SB. Control of domain-wall injection field with different nucleation pad geometry. J Nanosci Nanotechnol 2011; 11:6476-6478. [PMID: 22121739 DOI: 10.1166/jnn.2011.4482] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/31/2023]
Abstract
It is experimentally reported herein that the injection field of domain walls (DWs) from the nucleation pad to the nanowire is controlled by the angle of the initializing magnetic field with the use of asymmetric sample structures. The injection field is abruptly varied twice between two distinct values at a certain angle. Micromagnetic simulation is used to model the injection of a DW into the nanowire with respect to the angle of the initializing magnetic field. This is ascribed to the different structure of the DW at the junction between the pad and the nanowire, resulting in the different pinning strength of the DW. These observations provide a way to control the injection field of DWs into nanostructures and give a possibility of the fast, reliable motion of the DW with field strengths less than the so-called Walker field on the nanowire by injecting the DW with a known magnetic structure.
Collapse
Affiliation(s)
- Sung-Min Ahn
- Department of Physics, Seoul National University, Seoul 151-747, Republic of Korea
| | | | | | | |
Collapse
|
17
|
Ahn SM, Moon KW, Cho CG, Choe SB. Control of domain wall pinning in ferromagnetic nanowires by magnetic stray fields. Nanotechnology 2011; 22:085201. [PMID: 21242625 DOI: 10.1088/0957-4484/22/8/085201] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/30/2023]
Abstract
We have found that the depinning field of domain walls (DWs) in permalloy (Ni(81)Fe(19)) nanowires can be experimentally controlled by interactions between magnetic stray fields and artificial constrictions. A pinning geometry that consists of a notch and a nanobar is considered, where a DW traveling in the nanowire is pinned by the notch with a nanobar vertical to it. We have found that the direction of magnetization of the nanobar affects the shape and local energy minimum of the potential landscape experienced by the DW; therefore, the pinning strength strongly depends on the interaction of the magnetic stray field from the nanobar with the external pinning force of the notch. The mechanism of this pinning behavior is applied for the instant and flexible control of the pinning strength with respect to various DW motions in DW-mediated magnetic memory devices.
Collapse
Affiliation(s)
- Sung-Min Ahn
- Department of Physics, Seoul National University, Seoul, Republic of Korea.
| | | | | | | |
Collapse
|
18
|
Kim KJ, Moon KW, Lee KS, Choe SB. Control of magnetic domain-wall polarization by means of angled Oersted field writing. Nanotechnology 2011; 22:025702. [PMID: 21135480 DOI: 10.1088/0957-4484/22/2/025702] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/30/2023]
Abstract
We propose a method to control the polarization of the magnetic domain walls (DWs) in ferromagnetic nanowires. Two neighboring DWs with antiparallel polarization alignment rather than parallel alignment are found to exhibit better stability with a helical magnetic structure that can be hardly be detangled. To achieve such an antiparallel alignment, two co-planar current lines with an angle to the nanowire are designed, from which the Oersted field creates a domain in between the current lines while keeping the polarization of the DWs beneath the current lines, as confirmed by a micromagnetic calculation for ferromagnetic nanowires with perpendicular magnetic anisotropy.
Collapse
Affiliation(s)
- Kab-Jin Kim
- Department of Physics, Seoul National University, Seoul, Republic of Korea
| | | | | | | |
Collapse
|
19
|
Moon KW, Lee JC, Choe SB, Shin KH. Determination of perpendicular magnetic anisotropy in ultrathin ferromagnetic films by extraordinary Hall voltage measurement. Rev Sci Instrum 2009; 80:113904. [PMID: 19947739 DOI: 10.1063/1.3262635] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/28/2023]
Abstract
A magnetometric technique for detecting the magnetic anisotropy field of ferromagnetic films is described. The technique is based on the extraordinary Hall voltage measurement with rotating the film under an external magnetic field. By analyzing the angle-dependent Hall voltage based on the Stoner-Wohlfarth theory, the magnetic anisotropy field is uniquely determined. The present technique is pertinent especially for ultrathin films with strong intrinsic signal, in contrast to the conventional magnetometric techniques of which the signal is in proportion to the sample volume and geometry.
Collapse
Affiliation(s)
- Kyoung-Woong Moon
- School of Physics, Seoul National University, Seoul 151-742, Republic of Korea
| | | | | | | |
Collapse
|
20
|
Ko SH, Song KH, Park SA, Kim SR, Cha BY, Son HY, Moon KW, Yoo KD, Park YM, Cho JH, Yoon KH, Ahn YB. Cardiovascular autonomic dysfunction predicts acute ischaemic stroke in patients with Type 2 diabetes mellitus: a 7-year follow-up study. Diabet Med 2008; 25:1171-7. [PMID: 19046195 DOI: 10.1111/j.1464-5491.2008.02567.x] [Citation(s) in RCA: 46] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/25/2022]
Abstract
AIMS We investigated whether cardiovascular autonomic neuropathy (CAN) is associated with acute ischaemic stroke in patients with Type 2 diabetes. METHODS From 1999 to 2000, cardiovascular autonomic function tests were conducted in patients with Type 2 diabetes (n = 1458). Patients were followed up between 2006 and 2007. Standard tests for CAN measured heart rate variability parameters [expiration-to-inspiration (E/I) ratio, responses to the Valsalva manoeuvre and standing]. Using the American Diabetes Association criteria, the CAN scores were determined from the results of each test as follows: 0 = normal, 1 = abnormal (total maximum score 3). We assessed the development of acute ischaemic stroke events. RESULTS The prevalence of CAN at baseline was 55.7% (E/I 17.1%, Valsalva 39.4%, posture 27.3%) (n = 1126). During follow-up, 131 patients (11.6%) developed acute ischaemic stroke. The vascular events were more frequent in older patients (P < 0.001) and in those with diabetes of longer duration (P = 0.022), hypertension (P < 0.001) or diabetic retinopathy (P = 0.03) than in patients without vascular events. Patients with ischaemic stroke had higher creatinine levels (P = 0.045) and higher urine albumin excretion (P = 0.025) than those of patients without stroke. Cox proportional hazard regression analysis revealed that the CAN score was associated with the development of acute ischaemic stroke (total score 0 vs. 3, adjusted hazard ratio 2.7, 95% CI 1.3-5.5, P = 0.006). CONCLUSION Cardiovascular autonomic dysfunction was significantly associated with the development of ischaemic stroke in patients with Type 2 diabetes.
Collapse
Affiliation(s)
- S H Ko
- Division of Endocrinology and Metabolism, Department of Internal Medicine, The Catholic University of Korea, Seoul, Korea
| | | | | | | | | | | | | | | | | | | | | | | |
Collapse
|