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[2009] Argon National Laboratory (ANL) 초청강연 및 공동연구 논의 (host: Axel Hoffman)

Argon National Laboratory (ANL) 초청강연 및 공동연구 논의 (host: Axel Hoffman) - Invited talk

장소 : Argon National Laboratory (ANL), Chicago, USA
일정 : 2009년 9월 30일
제목 : Frontiers of the dynamics of vortices in magnetic nanostructures
발표자 : Sang-Koog Kim

초록 :
Ultrafast switching of the polarity of a magnetic vortex in soft magnetic nanodots has rapidly been growing in interest [1-2] due to its stable core magnetization of either upward or downward orientation and its applications to nonvolatile memory devices. Also, self-sustained vortex oscillators have begun to attract considerable attractions due to several advantages over spin-transfer-torque (STT) driven nano-oscillators[3].
In this talk, I will give a brief review of recently found vortex dynamics, including ultrafast vortex-core switching [2] and vortex-core gyrotropic motion [4] driven by linearly oscillating and circularly rotating in-plane fields or currents. This talk will cover the latest results of my group, self-sustained vortex oscillation and switching of both vortex-polarity and –chirality, which are driven by spin-polarized out-of-plane DC or pulse currents with extremely low current densities[3]. In more details, I will present the quantitative interpretations of the origins and mechanisms of those novel phenomena through analytical calculations and numerical simulations, considering both the STT and the Oersted field effects accompanying current flows. More specifically, two phase diagrams of the threshold current density and eigenfrequency of the steady-state vortex oscillations with respect to the dot thickness and radius [3], as well as the phase diagram of vortex-polarity and -chirality switching with respect to the dot dimensions and the transition current density will be presented, along with their detailed mechanisms.
These results provide an advanced step towards the practical applications of an array of vortex-state nanodots for new classes of vortex random access memory and nano-oscillators[5]. This work is supported by Creative Research Initiatives (ReC-SDSW) of MEST/KOSEF.

References:
[1] B. Van Waeyenberge et al., Nature 444, 461 (2006);R. Hertel et al., Phys. Rev. Lett. 98, 117201 (2007).
[2] K.-S Lee et al., Phys. Rev. B 76 174410 (2007); K. Y. Guslienko et al., Phys. Rev. Lett. 100, 027203 (2008); S.-K. Kim et al., Appl. Phys. Lett. 91, 082506 (2007); Ki-Suk Lee et al., Phys. Rev. Lett. 101, 267206 (2008).
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[2009] 11th International Conference on Advanced Materials (ICAM 2009)

11th International Conference on Advanced Materials (ICAM 2009) - Invited talk

장소 : Rio de Janeiro, Brazil
일정 : 2009년 9월 20일 ~ 25일
제목 : Vortex Dynamics in Confined Magnetic Nanodots
발표자 : Sang-Koog Kim

초록 :
Since spiraling magnetization configurations in patterned soft magnetic dots - the so-called magnetic vortices were experimentally observed [1], it has rapidly been a growing interest due to its stable core magnetization of either upward or downward orientation. Furthermore, recent studies on ultrafast switching of the vortex cores driven by oscillating or pulsed magnetic fields [2-8] and currents [9,10] with extremely low power provide opportunities for the practical applications for nonvolatile memory devices[11].
In this presentation, I will review recent findings on novel dynamic properties of vortex-core switching from the experimental and numerical studies, including the mechanism [4-5], the physical origin [6], and the universal criterion [7] from the fundamental perspective. I will further discuss the universal phase diagram with respect to the frequency and strength of circularly rotating fields from the technological point of view [7]. Moreover, I report a conceptual design of the new class of an information storage device, vortex random access memory (VRAM), on the basis of an array of vortex-state nanodots [8,11].
This work offers physical understandings of vortex dynamics in depth and the reliable means of information recording and readout which practically make the concept of VRAM possible. This work was supported by Creative Research Initiatives (ReC-SDSW) of MEST/KOSEF.

References:
e-mail: sangkoog@snu.ac.kr
[1] T. Shinjo et al.,, Science 289, 930 (2000).
[2] B. Van Waeyenberge et al., Nature 444, 461 (2006).
[3] Q. F. Xiao et al., J. Appl. Phys. 102, 103904 (2007).
[4] R. Hertel et al., Phys. Rev. Lett. 98, 117201 (2007).
[5] K.-S Lee, K. Y. Guslienko, J.-Y. Lee, and S.-K. Kim, Phys. Rev. B 76, 174410 (2007).
[6] K. Y. Guslienko, K.-S. Lee, and S.-K. Kim, Phys. Rev. Lett. 100, 027203 (2008).
[7] K.-S. Lee et al., Phys. Rev. Lett. 101, 267206 (2008).
[8] K.-S. Lee and S.-K. Kim, Phys. Rev. B. 78, 014405 (2008).
[9] K. Yamada et al., Nature Mater. 6, 269 (2007).
[10] S.-K. Kim et al., Appl. Phys. Lett. 91, 082506 (2007).
[11] S.-K. Kim, K.-S. Lee, Y.-S. Yu, and Y.-S. Choi, Appl. Phys. Lett. 92, 022509 (2008).
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[2009] Magnonics: From Fundamentals to Applications

Magnonics: From Fundamentals to Applications - Invited talk

장소 : Max-Planck-Institut fur Physik komplexer Systeme, Germany
일정 : 2009년 8월 2일 ~ 7일
제목 : Magnonic crystal waveguides of width-modulated thin-film nanostrips for an efficient broad-band spin-wave filter
발표자 : Sang-Koog Kim
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[2009] ALS/CXRO Seminar Series

ALS/CXRO Seminar Series - Invited talk

장소 : 6-2202 Conf Rm, Lawrence Berkeley National Lab (LBNL), Berklee, USA
일정 : 2009년 4월 29일
제목 : Ultrafast dynamics of magnetic vortices in nanodots: from fundamental to application
발표자 : Sang-Koog Kim

초록 :
Recently, ultrafast switching of the tiny core of a magnetic vortex in soft magnetic dots of submicron size or less has rapidly been growing in interest [1-11] due to its stable core magnetization of either upward or downward orientation, which is applicable for nonvolatile memory devices.
In this talk, I will review recent findings on novel dynamic properties of the vortex-core switching from experimental and numerical simulation studies, which include the mechanism [4-5], the physical origin [6], and the universal criterion [7] from the fundamental perspective. I will further discuss the universal phase diagram with respect to the frequency and strength of circularly rotating fields from the technological point of view, which is crucial for designs of the new class of an information storage device, vortex random access memory (VRAM), on the basis of an array of vortex-state nanodots [8,11].
These findings offer physical understandings of vortex dynamics in depth and the reliable means of information recording and readout which may make the concept of VRAM practically possible.
This work was supported by Creative Research Initiatives (ReC-SDSW) of MEST/KOSEF.

References:
[1] T. Shinjo et al.,, Science 289, 930 (2000).
[2] B. Van Waeyenberge et al., Nature 444, 461 (2006).
[3] Q. F. Xiao et al., J. Appl. Phys. 102, 103904 (2007).
[4] R. Hertel et al., Phys. Rev. Lett. 98, 117201 (2007).
[5] K.-S Lee, K. Y. Guslienko, J.-Y. Lee, and S.-K. Kim, Phys. Rev. B 76, 174410 (2007).
[6] K. Y. Guslienko, K.-S. Lee, and S.-K. Kim, Phys. Rev. Lett. 100, 027203 (2008).
[7] K.-S. Lee et al., Phys. Rev. Lett. 101, 267206 (2008).
[8] K.-S. Lee and S.-K. Kim, Phys. Rev. B. 78, 014405 (2008).
[9] K. Yamada et al., Nature Mater. 6, 269 (2007).
[10] S.-K. Kim et al., Appl. Phys. Lett. 91, 082506 (2007).
[11] S.-K. Kim, K.-S. Lee, Y.-S. Yu, and Y.-S. Choi, Appl. Phys. Lett. 92, 022509 (2008).
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[2008] 서강대학교 물리학과 초청강연 (국내)

서강대학교 물리학과 초청강연 (국내) - invite talk

장소: 서강대학교
일정: 2008년 10월 28일
주제: 스핀이란 과연 무엇일까?
발표자: 김상국
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[2008] Asian Forum on Magnetic (AFM 2008)
Asian Forum on Magnetic (AFM 2008) - invited talk

장소: Beijing, China
일정: 2008년 10월 16일 ~ 10월 18일
제목: Magnetic vortex dynamics: From fundamentals to applications
발표자:
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[2008] Join European Magnetic Symposia (JEMS 2008)

2008 Join European Magnetic Symposia (JEMS 2008) - Invited talk

장소 : Dublin, Ireland
일정 : 2008년 9월 14일 ~ 19일
제목 : Vortex-core reversal dynamics : From fundamentals to applications
발표자 : Sang-Koog Kim, Ki-Suk Lee, Young-Sang Yu, Youn-Seok Choi,Konstantin Yu Guslienko, June-Young Lee, and Hyeon-Seong Jeong, Dae-Eun Jung

초록 :
The magnetic vortex (MV) is now a well-known magnetic microstructure typically observed as ground and/or dynamic states in patterned or continuous soft magnetic thin films. The MV consists of two parts: One is the in-plane curling magnetizations as most part and the other is the out-of-plane magnetizations at the tiny core region, so called the vortex core (VC). The VC has either upward or downward magnetization orientation, so that it can be used as information carrier of binary digits “0” and “1”. Over the past five years, our group has found the nontrivial novel dynamic properties of magnetic vortices in geometrically confined magnetic thin-film dots[1], such as ultrafast vortex-core reversals by oscillating magnetic fields and currents with extremely low power and by circularly rotating fields in the film plane, its detailed mechanism, physical origin, universal criterion, as well as linear and nonlinear gyrotropic motions. On the basis of those novel static and dynamics properties of vortices, we propose a conceptual design of new classes of nonvolatile random access memory (RAM) using magnetic vortex arrays. In particular, the use of circular rotational fields of frequencies close to the eigenfrequecy of a given vortex allows us to select a vortex for its core reversal and detecting its core orientation for information recording and writing, respectively, with low power consumption as small as 10 Oe, and with excluding transistors assigned to individual cells for reliable writing and reading operation [2].
 The results provide a new as well as more detailed physical understanding of vortex-related dynamics in soft magnetic nanodots, and allow for an effective manipulation of vortex motions and VC switching, as well as its practical application to information storage devices such as vortex-RAM (VRAM) coined by us, for the first time. This work was supported by Creative Research Initiatives (ReC-SDSW) of MOST/KOSEF

References
[1] K.-S. Lee, K. Y. Guslienko, J.-Y. Lee, S. -K. Kim, Phys. Rev. B, 76 174410 (2007).
[2] S.-K. Kim, K.-S. Lee, Y.-S. Yu, Y.-S. Choi, Appl. Phys. Lett., 92 022509 (2008).
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[2008] The 6th International Workshop

The 6th International Workshop - Invited talk

장소: Hanyang University, Seoul, Korea
일정: 2008년 8월 13일
제목: Magnetic vortex core reversal dynamics and applications
발표자: Sang-Koog Kim, Ki-Suk Lee, Youn-Seok Choi, Young-Sang Yu, Konstantin Yu Guslienko, and Hyunsung Jung

초록:
The magnetic vortex has the in-plane curling magnetizations along with the out-of-plane magnetizations at the core, the so-called vortex core (VC). The VC has either upward or downward magnetization orientation so that it can be used as an information carrier of the binary digits “0” and “1”. Over the past five years, our group has found nontrivial novel dynamic properties of magnetic vortices in geometrically confined magnetic thin-film dots, such as ultrafast vortex-core reversal driven by oscillating magnetic fields or spin-polarized currents with extremely low power, and driven by circularly rotating fields in the film plane. In addition, the detailed mechanism, physical origin, universal criterion of vortex core reversals, and the elementary eigenmodes of the linear gyrotropic motions of magnetic vortices, and their linear and nonlinear behaviors have been found from our previous works.
In the present talk, we report on a new as well as deeper fundamental understanding of vortex dynamics in soft magnetic nanodots, as well as report on an effective manipulation of vortex motions and VC switching with extremely low power. Moreover, on the basis of those aforementioned novel static and dynamic properties, we propose a conceptual design of new class information storage devices such as vortex random access memory (VRAM) using an array of dots in the vortex states. We address the scheme of the proposed VRAM in relation to the feasibility of its realization as a future solid-state information storage device. This work was supported by Creative Research Initiatives (ReC-SDSW) of MEST/KOSEF.
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[2008] Moscow International Symposium on Magnetism (MISM 2008)

Moscow International Symposium on Magnetism (MISM 2008) - Invited talk

장소: M.V Lomonosov Moscow State University, Moscow, Russia
일정: 2008년 6월 20일 ~ 25일
제목: VORTEX-CORE REVERSAL DYNAMICS AND VORTEX RANDOM ACCESS MEMORY
발표자: Sang-Koog Kim, Ki-Suk Lee, Youn-Seok Choi, Young-Sang Yu, and Hyeon-Seong Jeong

초록:
The magnetic vortex (MV) is now a well-known magnetic microstructure typically observed as ground and/or dynamic states in patterned [1] or continuous soft magnetic thin films [2]. The MV consists of two parts: One is the in-plane curling magnetizations as most part and the other is the out-of-plane magnetizations at the tiny core region, so called the vortex core (VC). The VC has either upward or downward magnetization orientation, so that it can be used as information carrier of binary digits “0” and “1” [3]. Over the past five years, our group has found the nontrivial novel dynamic properties of magnetic vortices in geometrically confined magnetic thin-film dots, such as ultrafast vortex-core reversals by oscillating magnetic fields and currents with extremely low power and by circularly rotating fields in the film plane, its detailed mechanism [4], physical origin [5], universal criterion [6], as well as linear and nonlinear gyrotropic motions [7]. On the basis of those novel static and dynamics properties of vortices, we propose a conceptual design of new classes of nonvolatile random access memory (RAM) using magnetic vortex arrays. In particular, the use of circular rotational fields of frequencies close to the eigenfrequecy of a given vortex allows us to select a vortex for its core reversal and detecting its core orientation for information recording and writing, respectively, with low power consumption as small as 10 Oe, and with excluding transistors assigned to individual cells for reliable writing and reading operation [3].
 The results provide a new as well as more detailed physical understanding of vortex-related dynamics in soft magnetic nanodots, and allow for an effective manipulation of vortex motions and VC switching, as well as its practical application to information storage devices such as vortex-RAM (VRAM) coined by us, for the first time.


Supported by Creative Research Initiatives (ReC-SDSW) of MOST/KOSEF

[1] T. Shinjo, T. Okuno, R. Hassdorf, K. Shigeto, T. Ono, Science, 289 (2000) 930.
[2] S.-K. Kim, K.-S. Lee, B.-W. Kang, K.-J. Lee, J. B. Kortright, Appl. Phys. Lett., 86 (2005) 052504.
[3] S.-K. Kim, K.-S. Lee, Y.-S. Yu, Y.-S. Choi, Appl. Phys. Lett., 92 (2008) 022509.
[4] K.-S. Lee, K. Y. Guslienko, J.-Y. Lee, S. -K. Kim, Phys. Rev. B, 76 (2007) 174410 .
[5] K. Y. Guslienko, K.-S. Lee, S.-K. Kim, Phys. Rev. Lett., 100 (2008) 027203.
[6] S.-K. Kim, Y.-S. Choi, K.-S. Lee, K. Y. Guslienko, D.-E. Jeong, Appl. Phys. Lett., 91 (2007) 082506.
[7] K.-S. Lee, S.-K. Kim, Appl. Phys. Lett., 91 (2007) 132511.
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[2008] International Workshop on Nano-structured Materials & Magnetics(NMM 2008)

[2008] International Workshop on Nano-structured Materials & Magnetics(NMM 2008) - Invited talk

장소: University of the Ryukyus, Okinawa, Japan
일정: 2008년 2월 10일 ~ 11일
제목: Ultrafast Vortex-Core Reversal and Application to Information Storage
발표자: Sang-Koog Kim, Ki-Suk Lee, Young-Sang Yu, Konstantin Yu Guslienko, Youn-Seok Choi (Seoul National University)

초록:
The magnetic vortex (MV) is now a well-known magnetic microstructure that is typically observed as a ground state in patterned(1) or continuous soft magnetic thin films(2). The MV consists of the in-plane curling magnetizations as most part and the out-of-plane magnetizations at its core region, so called vortex core (VC). The VC has either upward or downward magnetization direction so that it can be used as information carrier as binary digit “0” or “1” (3). From a practical application point of view, the remaining issue is then how to switch the VC orientation with low power consumption and how to make votices practially applicalbe to information storage device as well. In this talk, we will present VC related dynamics such as the linear and nonlinear gyrotropic motion(4), as well as the physical origin(5) and detailed mechanism(6) of the VC reversal (switching), and the universal criterion(7). In addition, we will report a conceptual desgin of a new class of nonvolatile random access memory using vortex arrays based on the nontrivial dynamic properties.
In the present work, we conducted micromagnetic numerical calculations, using the LLG equation of motion, of the dynamic responses of a ground vortex state in Permalloy (Py) cylindrical dots of various dimensions to oscillating in-plane linear and circular magnetic fields (and spin-polarized currents) over wide frequency and amplitude ranges.  It is found that five different kinds of non-trivial vortex dynamics are distingused according to the field frequency and amplutde, which include low-and high-amplitude gyrotropic motions and the periodic creation and annihilation of vortex-antivortex pair(6), etc. Here we focus on not only the vortex-core reversal regime (see Fig.1) but also the underlying physics such as the exact mechanism and physical origin of the ultrafast VC reversal on the 10 ps scale, and its generic criteria related to the critical velocity and elementary eigenmodes of the VC gyrotoropic motion (3) (7).
On the basis of those novel static and dynamics properties of vortices we found, we conceptually designed a new class of random access memory using magnetic vortex arrays. In particular, the use of circularly rotation fields of the frequencies close to the eigenfrequecy of a given vortex allows us to select a vortex that we want to switch and detect the VC orienation for information recording and writing, resepectively, with low power consumption as small as 10 Oe, and with excluding transistors assigned to individual cells for reliable writing and reading operation(3).
 The results to be presented in this talk provide a new as well as more detailed physical understanding of vortex-related dynamics in soft magnetic nanodots, and allow for an effective manipulation of vortex motions and VC switching, as well as its practical application to information storage devices such as vortex random access memory (VRAM), coined by us for the first time.

This work was supported by Creative Research Initiatives (Research Center for Spin Dynamics and Spin-Wave Devices) of MOST/KOSEF.

(1) T. Shinjo, T. Okuno, R. Hassdorf, K. Shigeto, and T. Ono : “Vortex Core Observation in Circular Dots of Permalloy”, Science 289, 930 (2000).
(2) S.-K. Kim, K.-S. Lee, B.-W. Kang, K.-J. Lee, and J. B. Kortright, “Vortex-antivortex assisted magnetization dynamics in a semi-continuous thin-film model system studied by micromagnetic simulations”, Appl. Phys. Lett. 86, 052504 (2005).
(3) S.-K. Kim, K.-S. Lee, Y.-S. Yu, and Y.-S. Choi : “Reliable low-power control of ultrafast vortex-core switching with the selectivity in arrays of vortex states by in-plane circular-rotational magneticfields and spin-polarized currents”, Appl. Phys. Lett. (in press)
(4) K.-S. Lee and S.-K. Kim : “Gyrotropic linear and nonlinear motions of a magnetic vortex core in soft magnetic nanodots”  Appl. Phys. Lett. 91. 132511 (2007)
(5) K. Y. Guslienko, K.-S. Lee, and S.-K. Kim : “Dynamic Origin of Vortex Core Switching in Soft Magnetic Nanodots”, Phys. Rev. Lett. (in press), e-print arXiv:cond-mat/0708.1359.
(6) K.-S. Lee, K. Y. Guslienko, J.-Y. Lee, and S. -K. Kim : “Ultrafast Vortex-Core Reversal Dynamics in Ferromagnetic Nanodots”, Phys. Rev. B 76, 174410 (2007)
(7) S.-K. Kim, Y.-S. Choi, K.-S. Lee, K. Y. Guslienko, and D.-E. Jeong, “Electric-current-driven vortex-core reversal in soft magnetic nanodots”, Appl. Phys. Lett. 91, 082506 (2007)
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[2007] 52nd Magnetism and Magnetic Materials Conference

[2007] 52nd Magnetism and Magnetic Materials Conference - Invited talk

장소 : Tampa, Florida, USA
일정 : 2007년 11월 5일 ~ 9일
제목 : Vortex Dynamics in Patterned Ferromagnetic Films: Gyromotion, Reversal, and Domain-Wall Transformation.
발표자 : S. Kim; K. Lee; J. Lee; K. Y. Guslienko; Y. Yu; Y. Choi; D. Jeong

초록:
In the research area of vortex-related magnetization dynamics in confined magnetic elements including nanodots, nanostripes, and others[1-9], challenging key research goals are the fundamental understanding of the eigenmodes of excitations of magnetic vortices (MVs), including the linear and nonlinear gyromotions, the true origin and detailed mechanism of the vortex-core (VC) reversal, its universal criteria, and the underlying physics of complex domain-wall (DW) transformations. To tackle the above-mentioned problems, we conducted micromagnetic simulations on different dynamic responses of MV states in Permalloy (Py) dots of various dimensions to oscillating in-plane linear and circular magnetic fields (and spin-polarized currents) over wide frequency and amplitude ranges. We also investigated DW motions in Py nanostripes by conducting micromagnetic simulations. In nanodots, we found five different kinds of non-trivial vortex dynamics such as low-and high-amplitude gyromotions and the periodic creation and annihilation of vortex-antivortex pairs[6]. Here we present vortex-related dynamic phenomena and the underlying physics such as the exact mechanism and true origin of the ultrafast VC reversal, its generic criteria related to the critical velocity, and VC elementary eigenmodes. On the ground of the MV dynamics, the problems of oscillatory DW motions are solved by considering the emission and absorption of vortex or antivortex through transverse wall, conserving the total topological charges during the DW transformation in the nanostripes[8]. To interpret those results, we formulated analytical equations of MV and DW motions according to motion of magnetic solitons in nanodots and nanostripes, respectively, and on the basis of a generalized Thiele equation[9], which accurately reproduces the simulation results of “VC trajectories in nanodots and nanostripes, and their frequency spectra.” The results provide a new and more detailed understanding of vortex-related dynamics in nanodots and nanostripes, and allow for an effective manipulation of vortex motions, VC switching, and periodic DW transformations.


[1] MVs are typically observed as ground states in patterned (or continuous) soft magnetic thin films. Since the MV gyromotion was verified theoretically [2] and experimentally [3], the non-trivial dynamic properties of MVs in nanoscale magnetic elements continue to attract considerable interest. Quite recently, resonant excitations of a VC and its related reversal, both driven by an oscillating in-plane magnetic field [4-6] and an AC current [7], were also experimentally verified. In addition, oscillatory DW motions in nanostripes become hot issues that are known to be related to dynamic transformations between the vortex (or antivortex) wall and the transverse wall during the propagation of a DW [8].
[2] K. Guslienko et al., J. Appl. Phys. 91, 8037 (2001).
[3] S. B. Choe et al., Science 304, 420 (2004).
[4] B. Van Waeyenberge et al., Nature 444, 461 (2006).
[5] S. Choi et al., Phys. Rev. Lett. 98, 087205.(2007).
[6] K.-S. Lee, K. Y. Guslienko, J.-Y. Lee, and S. -K. Kim, arXiv:cond-mat/0703538v1.
[7] S. Kasai et al., Phys. Rev. Lett. 97, 107204 (2006); K. Yamada et al., Nature Mater. 6. 296 (2007).
[8] J.-Y. Lee, K.-S. Lee, S. Choi, K. Y. Guslienko, and S.-K. Kim, arXiv:cond-mat/0706.2542v1.
[9] A. A. Thiele, Phys. Rev. Lett. 30, 230 (1973); D. L. Huber, Phys. Rev. B 26, 3758 (1982).

This work was supported by Creative Research Initiatives (Research Center for Spin Dynamics and Spin-Wave Devices) of MOST/KOSEF.
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[2007] The 10th Asia Pacific Physics Conference (APPC10)

주 제: Spin Waves in Restricted Geometry
일 시: 2007년 8월 21일(화요일) 오후 4:30
장 소: Conference Room D(2F), POSCO International Center, POSTECH
초 록: 

Spin-wave (SW) excitations in bulk and thin film ferromagnets have long been a fundamentally interesting topic in the research area of magnetism. Nowadays, SWs in confined magnetic elements such as nanodots, nanowires, and etc. are of revived interest, both theoretically and experimentally. Considerable progress in the understanding of spin excitation spectra in restricted geometries has been achieved with the help of theoretical approaches, and sub-ns time- and sub-micron space-resolving measurement techniques.
In this talk, we report the micromagnetic numerical and analytical studies of the radiation of spin waves with large amplitudes produced by an in-plane magnetic-pulse-field induced reversal of a magnetic vortex core, as well as their wave behaviors in magnetic nanowires. It was found that the radial SWs can be emitted intensively from a vortex core in a circular dot due to its field-induced reversal, and then can be injected into nanowires. Our results demonstrate the radiation behavior of SWs produced from a magnetic vortex core associated with its reversal, the injection behavior of SWs from a circular dot into nanowire waveguides, and how to control the frequencies of SWs using nanowire-type heterostructures. These are key points in understanding the fundamental wave properties of SWs in restricted geometry, such as their radiation, propagation, reflection, transmission, interference, dispersion, and filtering of specific frequencies. The results offer a preview of the generation, delivery, and manipulation of SWs in nano-size patterned magnetic elements.
This work was supported by Creative Research Initiatives (ReC-SDSW) of MOST/KOSEF.

Keywords : spin wave, nanowire, radiation, magnetic vortex, magnonic crystal, propagation 
 
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[2007] the Seminar of the Materials Science Division, Argonne National Laboratory

장소 : Argonne National Laboratory (Argonne, Illinois, U.S.)
일정 : 2007년 5월 7일(월)
제목 : Radiation of Spin Waves by Vortex Core Reversal in Magnetic Nanoelements
발표자 : Konstantin Guslienko and Sang-Koog Kim
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[2007] 한국외국어 대학교 전자물리학과 초청세미나 (국내)

장소 : 물리학과 세미나실(318-1호)
일정 : 2007년 4월 5일(木) 12:20~1:10
Host : 정창욱
제목 : 스핀이란 과연 무엇일까?
발표자 : 김상국 교수

내용 : 막대 자석은 무엇으로 이루어졌을까? 왜 지구는 자기력을 만들어 낼까? 우리주변에 자석과 자기력을 이용한 소자는 어떤 것이 있을까? 주위에서 볼 수 있는 자연현상 중에 자기 힘과 관련된 현상은 신비한 마술과 같아서 일반인의 호기심을 끌기에 충분하다. 자기 성질을 나타내는 물질은 산소를 운반하는 혈액, 박테리아, 철분이 많이 함유된 씨리얼에도 존재한다. 우리가 살고 있는 지구는 거대한 자석이다.  자기와 관련된 자연현상은 지구상에 존재하는 동식물의 생명활동에 어떤 영향을 미치는 것일까?  본 세미나에서는 생명활동에 필요한 자성체부터 인류의 지식기반 사회를 풍요롭게 하는 자기 소재/소자에 대해 소개하겠다. 또한 거대 은하, 블랙홀, 토네이도 등의 소용돌이 형상과 흡사한 자성체에서 볼 수 있는 소용돌이 구조를 소개하고 그 응용성을 찾아본다. 
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[2007] KAIST 물리학과 봄학기 콜로키움 (국내)

주제: 스핀의 세계
일시: 2007년 3월 26일(월) 4:00
장소: KAIST 자연과학동 공동강의실
발표자 : 김상국 교수
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