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[2014] The 3rd international conference of AUMS (IcAUMS 2014)

The 3rd international conference of AUMS (IcAUMS 2014)

 

장소 : Hainan international convention and exhibition center, Haikou, China
일정 : 2014년 10월 28일 ~ 2014년 11월 2일
주제 : Coupled Vortex Dynamics in One-dimensional Vertex Lattices
발표자 : Sang-koog Kim
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[2013] International symposium on ecotopia science 2013 (ISETS '13)

International symposium on ecotopia science 2013 (ISETS '13)

 

장소 : Nagoya university, Nagoya, Japan
일정 : 2013년 12월 13일 ~ 2013년 12월 15일
주제 : Magnonic crystals based on coupled vortex-core gyration
발표자 : D.Han
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[2012] 제 24차 방사광 이용자 연구발표회 및 협회정기총회

제 24차 방사광 이용자 연구발표회 및 협회정기총회

 

장소 : 포스코 국제관, 포항공대내
일정 : 2012년 11월 22일
주제 : Coupled vortex gyrations in nanomagnet networks
발표자 : Sang-koog Kim

 

초록 :

In current semiconductor technologies of information storage and processing devices, the electron charge is the basic operational unit. However, the significant electron leakage, with the inevitable energy loss, in cases of nanoscale electron channels, is a major limitation of this technology. Additional research into new, practical alternatives, therefore, is a priority. One
such alternative is to use switchable magnetization states in nanomagnet networks [1]. In this presentation, our group and colleagues propose a robust mechanism of information signal transfer based on magnetic-vortex-state networks and experimentally measure coupled vortex oscillations by a state-of-the-art measurement probe, soft X-ray transmission microscopy through XMCD contrast [1-3]. Herein, collective vortex gyration modes, as studied and elucidated by micromagnetic simulations and analytical derivations, vary with different polarization and chirality ordering between neighboring disks [1,4,5]. The advantages of this mechanism are unlimited signal transfer endurance, low energy dissipation, and low-power signal inputs via resonant vortex excitation [5]. This work paves the way for novel, magneticvortex-state-networks-based signal transfer and logic operations applicable to spin-based information-signal-processing devices.

 


[1] H. Jung et al., Scientific Reports(NPG), 1, 59; DOI:10.1038/srep00059 (2011).
[2] H. Jung et al., Appl. Phys. Lett., 97, 222502 (2010).
[3] H. Jung et al., ACS Nano, DOI: 10.1021/nn3000143(2012) .
[4] K.-S. Lee et al., J. Appl. Phys., 110, 113903 (2011).
[5] J.-H. Kim, et al., Appl. Phys. Lett. 101, 092403 (2012).
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[2012] International Advanced School on Magnonics

International Advanced School on Magnonics

 

장소 : Hotel Regina elena, Santa Margherita Ligure, Italy
일정 : 2012년 9월 3일 ~ 2012년 9월 7일
주제 : Magnonic crystals and possible logic gates
발표자 : Sang-koog Kim
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[2012] International Workshop On Novel Nanomagnetic & Multifunctional Material 2012-Intited talk

International Workshop On Novel Nanomagnetic & Multifunctional Material 2012-Intited talk

장소 : Sheraton Walkerhill Hotel, Seoul, Korea
일정 : 2012년 6월 11일 ~ 2012년 6월 14일
주제 : A robust new mechanist of information-signaltransfer: coupled vortex gyrations in nanomagnet networks
발표자 : Sang-koog Kim

초록:
In current semiconductor technologies of information storage and processing devices, the electron charge is the basic operational unit. However, the significant electron leakage, with the inevitable energy loss, in cases of nanoscale electron channels, is a major limitation of this technology. Additional research into new, practical alternatives, therefore, is a priority. One such alternative is to use switchable magnetization states in nanomagnet networks [1-3]. In this presentation, I propose a robust mechanism of information signal transfer and logic operations based on magnetic-vortex-state networks; further, I report experimental demonstrations of the concept prototype for an archetypal logic operation. The advantages of this mechanism are unlimited signal transfer endurance, low energy dissipation, and lowpower signal inputs via resonant vortex excitation. Additionally, I introduce a new type of magnonic crystals comprised of one- and two-dimensional arrays of dipolarcoupled vortex-state nanodisks. Herein, collective vortex gyration modes, as studied and elucidated by micromagnetic simulations and analytical derivations, vary with different polarization and chirality ordering between neighboring disks. This work paves the way for novel, magnetic-vortex-state-networks-based signal transfer and logic operations applicable to spin-based information-signal-processing devices. The present study was supported by the Basic Science Research Program through the National Research Foundation of Korea (NRF) funded by the Ministry of Education,Science and Technology.

References:
[1] H. Jung et al., Scientific Reports, 1, 59; DOI:10.1038/srep00059 (2011).
[2] H. Jung et al., Appl. Phys. Lett., 97, 222502 (2010).
[3] K.-S. Lee et al., J. Appl. Phys., 110, 113903 (2011).
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[2011] The 7th International Conference on Advanced Materials and Devices

[2011]The 7th International Conference on Advanced Materials and Devices -Invited talk

장소: 라마다프라자 제주호텔, 제주
일정: 2011년 12월 7일 ~ 2011년 12월 9일
주제: Vortex-gyration-mediated information-signal transfer in vortex-state magnet networks
발표자:  Sang-Koog Kim

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[2011] 한국자기학회 2011년 동계학술대회

[2011] 한국자기학회 2011년 동계학술대회 - Invited talk

장소: 라마다프라자 제주호텔, 제주
일정: 2011년 12월 5일 ~ 2011년 12월 7일
주제: Micromagnetic simulations based on directly observed microstructures
발표자: Jehyun Lee and Sang-Koog Kim

초록:

1. Introduction

In recent years, micromagnetics has been the most popular numerical method in the field of magnetic recording owing to its fast, reliable and economic way of study1. Introduction of the finite element method (FEM) to micromagnetics has enabled us to take into consideration of the real microstructures, such as granular structure with irregular grain shape and distributions, soft/hard phase dispersions and local defects in order to find the contribution to magnetic behaviors2-6. In order to implement the microstructure of a given specimen into finite element models, investigation of the microstructure using X-ray diffraction (XRD) analysis or transmission electron microscopy (TEM) study is the prerequisite, as well as the material parameters measured by proper experiments, i.e. vibrating sample magnetometry (VSM). Micromagnetic simulations based on the realistic microstructure are performed by assigning the magnetic parameters on the finite element models prepared based on the experimental findings. In this talk we are going to present a couple of examples of the micromagnetic simulations based on the directly observed microstructures, particularly on magnetic recording media: FePtCu L10 phase based bit patterned media7,8.

2. Experimental and Micromagnetic simulation details

FePtCu L10 thin film is prepared by deposition of FePt(4.7 nm) and Cu(0.3 nm) bilayer film using dc magnetron sputtering, then a sequential rapid thermal annealing (RTA) process for 30 seconds at 600oC under N2 atmosphere. The chemical composition of (Fe52Pt48)91Cu9 was determined by Rutherford Backscattering Spectroscopy (RBS), and the (001) texture perpendicular to the plane was revealed by XRD. 5 nm of Ta layer was deposited on top of the film as a hard mask for post-patterning process. Material parameters of Keff = 0.55 MJ/m3 and MS = 770 kA/m were determined from the hysteresis loop obtained by superconductive quantum interference device (SQUID). The FePtCu film is patterned to 30 nm diameter and 60 nm pitch using nanoimprint lithography. The geometry and microstructure of the bit paterned media, for example, bit size distribution and crystalline structures are studied using scanning electron microscopy (SEM) and TEM. In order to deeply understand the magnetization behaviors of the bit patterned media, finite element models are prepared following the findings from the electron microscopy, then micromagnetic simulations were performed on the models.

3. Experimental and Micromagnetic simulation results and discussion

Comparing the hysteresis loops obtained from the film and the patterned media, much larger coercivities and broader switching field distribution (SFD) are found in the pattenred media. Moreover, the angular dependency of the switching field was also deviated from the Kondorsky mode after patterning, but cannot be described by the Stoner-Wohlfarth model either. The microstructural investigations give us some clues on the origin of the changes in magnetic behaviors. From analysis of the SEM plan view image, the standard deviation of the bit diameters is 7 % of the mean value, this might be one of the origin of the SFD. From the TEM cross sectional studies, the shape of the bit is found to be a truncated cone, with a damage on the crystalline structure at the shoulder of the bits,with distributions in the easy axis alignment. We have assumed the deviation of the intrinsic parameters - easy axis alignement and anisotropy constant as well as the size distribution and damages on the lattice structures in micromagnetic simulations. The contributions of each sources on SFD have been studied quantitatively, finally summarized. The angular dependency was explained by inhomogeneous magnetization reversals owing to the damages on the specimen.

4. Summary

We have prepared FePtCu L10 bit patterned media, of which magnetic properties and microstructural details are obtained by direct measurement and observations. The patterning process on the continuous film induced a drastic changes in the coercivity, SFD, and angular dependencies. The origin of the changes are explained by micromagnetic simulations with the finite element models including the details of the microstructures.


5. References
1. J. Brown, William Fuller, Micromagnetics.(Interscience,1962).
2. T. Schrefl, J. Fidler, K. J. Kirk and J. N. Chapman, IEEE Trans. Magn. 33(5),4182-4184(1997).
3. T. R. Koehler, Physica B: Cond. Mat. 233(4),302-307(1997).
4. D. Fredkin and T. Koehler, IEEE Trans. Magn. 23(5),3385-3387(1987).
5. C. Seshan and Z. Cendes, IEEE Trans. Magn.21(6),2378-2381(1985).
6. D. Makarov, J. Lee, C. Brombacher, C. Schubert, M. Fuger, D. Suess, J. Fidler and M. Albrecht, Appl Phys Lett 96(6),062501(2010).
7. C. Brombacher, M. Grobis, J. Lee, J. Fidler, T. Eriksson, T. Werner, O. Hellwig and M. Albrecht, Nanotechnology in press (2011).
8. J. Lee, C. Brombacher, J. Fidler, B. Dymerska, D. Suess and M. Albrecht, Appl Phys Lett 99(6),062505(2011).
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[2011] 한국물리학회 2011년 가을학술논문발표회 및 임시총회

[2011] 한국물리학회 2011년 가을학술논문발표회 및 임시총회-Invited talk

장소: 벡스코, 부산
일정: 2011년 10월 19일 ~ 2011년 10월 21일
주제: Vortex-gyration-mediated Information-signal Transfer in Magnetic-vortex-state Networks: From Fundamental to Application  
발표자:  KIM Sang-Koog 

초록:
Low-energy input signals and their transport with low energy dissipation are the key technological factors in the design of information processing devices. Coupling between different oscillators allows for the possibility of mutual energy transfer between them and the information-signal propagation. Recently, it was found that stimulated vortex gyration is a robust new mechanism for energy transfer between spatially separated dipolar-coupled magnetic disks based on the concept of coupled vortex-core oscillators[1]. Here, I report on an experimental demonstration of coupled vortex gyrations and a numerical study of collective vortex gyration modes in one-dimensional vortex-state arrays of different vortex-state orderings. Moreover, I present examples of logic operations based on vortex-state networks and novel vortex-gyration-mediated energy-transfer phenomena. This mechanism provides the advantages of tunable energy transfer rate, low-power input signal, and extremely low energy dissipation for the case of using negligible damping materials.       
This work was supported by Basic Science Research Program through the National Research Foundation of Korea (NRF) funded by the Ministry of Education, Science and Technology. 

[1] H. Jung et al, Scientific Reports 1, 59; DOI:10.1038/srep00059 (2011).
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[2011] Moscow International Symposium on Magnetism
[2011]Moscow International Symposium on Magnetism - Invited talk

장소 : M. V. Lomonosov Moscow State University, Moscow, Russia
일정 : 2011년 8월 21일~2011년 8월 25일
제목 : Edge-soliton-mediated vortex-core reversal dynamics
발표자 : Ki-Suk Lee, Myoung-Woo Yoo, Youn-Seok Choi, and Sang-Koog Kim*

초록 :
In micrometer-size (or smaller) magnetic elements, magnetic topological solitons play their crucial roles in the dynamics of ultrafast magnetization reversals [1]. One of typical examples is a well-known vortex-antivortex-pair-mediated vortex-core reversal in nanodisks; vortex-core reversals take place through the creation and annihilation of a pair of a vortex and an antivortex bulk topological solitons [2-4] while conserving the total winding number topological charge of involved solitons. However, another topological charge, the Skyrmion number decays when a pair of vortex and antivortex annihilates. Thus, the exchange energy of the Skyrmion dissipates drastically through the exchange energy explosion and subsequent spin-wave emission [2-4]. In this presentation, we are going to report a new reversal mechanism of single vortex cores in magnetic disks driven by currents flowing perpendicular to the disk plane, as found from micromagnetic simulations [5]. This mechanism is totally different from the well-known vortex-antivortex pair mediated vortex core reversal in terms of the associated topological solitons, energies, and spin-wave emissions. In this mechanism, vortex core switching occurs through serial dynamic transformations from an initial vortex to a pair of two edge solitons, again back to a newly created vortex of reversed core orientation. In contrast to the vortex-antivortex pair mediated vortex core switching, the exchange energy of the Skyrmion does not dissipate drastically through the spin-wave emission but it converts to the strong magnetostatic energy of paired edge solitons. This work provides deeper physical insights into the dynamic transformations of magnetic topological solitons in magnetic nanoscale elements.
This work was supported by Basic Science Research Program through the National Research Foundation of Korea (NRF) funded by the Ministry of Education, Science and Technology (No. 20110000441).

Reference:
[1] N. D. Mermin, Rev. Mod. Phys. 51, 591 (1979); O. Tchernyshyov and G. Chern, Phys. Rev. Lett. 95, 197204 (2005).
[2] B. Van Waeyenberge et al., Nature 444, 461 (2006).
[3] Q. F. Xiao et al., Appl. Phys. Lett. 89, 262507 (2006);R. Hertel et al., Phys. Rev. Lett. 98, 117201 (2007).
[4] K.-S. Lee et al., Phys. Rev. B 78, 014405 (2008); K. Y. Guslienko, K.-S. Lee, and S.-K. Kim, Phys. Rev. Lett. 100, 027203 (2008); K.-S. Lee et al., Phys. Rev. Lett. 101, 267206 (2008).
[5] K.-S. Lee et al., Phys. Rev. Lett. 106, 147201 (2011).

 



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[2011] SPIE Optics + Photonics 2011

[2011]SPIE Optics + Photonics 2011-Invited talk

장소 : San Diego Convention Center,San Diego, California, USA
일정 : 2011년 8월 21일~ 2011년 8월 25일
제목 : Vortex-gyration-mediated information-signal transfer in one-dimensional arrays of soft magnetic nanodisks
발표자 : Sang-koog Kim, Dong-Soo Han

초록 :
Low-energy input signals and their transport with low-energy dissipation are the key technological factors in the design of information processing devices. Coupling between different oscillators allows for the possibility of mutual energy transfer between them and the information-signal propagation. Recently, it was found that stimulated vortex gyration is a robust new mechanism for energy transfer between spatially separated dipolar-coupled magnetic disks based on the concept of coupled vortex-core oscillators. The rate of energy transfer from one disk to the other is determined by the two normal modes’ frequency splitting caused by dipolar interaction. Here, we present collective vortex gyration modes in one-dimensional arrays of dipolar coupled vortex-state nanodisks, as studied from micromagnetic simulations and analytical derivations of their characteristic band structures that vary with the relative polarization states. The quantized mode can be referred to as “vortex gyraton”. This mechanism provides the advantages of tunable energy transfer rate, low-power input signal, and low-energy dissipation for magnetic elements with negligible damping. Coupled vortex-state disks might be implemented in applications for information-signal processing.
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[2011] March Meeting of APS

March Meeting of APS -Invited talk

 


장소 : Dallas Convention Center, Dallas,Texas, USA

일정 : 2011년 3월 21일~2011년 3월 25일

제목 : Vortex-Core Reversal Dynamics: Towards Vortex Random Access Memory

발표자 : Sang-Koog Kim
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[2010] International Conference of AUMS (ICAUMS 2010)

[2010] International Conference of AUMS (ICAUMS 2010) - Invited talk

장소: Jeju Island, Korea
일정: 2010년 12월 5일 ~ 2010년 12월 8일
제목: Unipolar Gaussian-pulse current driven vortex core switching in cross-point architecture
발표자: Young-Sang Yu, Ki-Suk Lee, Hyunsung Jung, Youn-Seok Choi, Jun-Young Lee, Myoung-Woo Yoo, Dong-Soo Han, Mi-Young Im, Peter Fischer and Sang-Koog Kim*

초록:
The magnetic vortex in patterned soft magnetic elements has been considered to be a potential candidate for information storage due to its core binary states, as well as energetically very stable configurations [1]. Recently, vortex core switching by oscillating linear, rotating fields or pulses with low-power consumption [2] has stimulated further studies towards implementation of the magnetic vortex into actual nonvolatile magnetic random access memory [3]. In this word, se conducted experimentally vortex core switching driven by specially designed pulse-type rotating fields available with two orthogonal and unipolar Gaussian-pulse currents. The width (σ) and time delay (Δt) were analytically and numerically optimized to be σ = 1/ωD and Δt = π /(2ωD) with eigenfrequency ωD. Vortex-core switching events sere measured after applications of such pulse type rotating fields of different values of the amplitude (H0), σ, and Δt, using a full-field soft x-ray transmission microscope (on beamline 6.1.2, Advanced Light Source) [4]. The threshold field strength for vortex core switching varies significantly with Δt and σ.  The experimental results present that the reliable control of vortex-core-orientation-selective switching simply by adjusting the sign of Δt are possible even with two orthogonal and unipolar current pulses. The optimal values of σ and Δt are in good agreements with the experimental results as well. Based on the low-power consumption switching, we also demonstrated a reliable selection and switching of memory cells by choosing the bit-and word-line electrodes in two-by-two vortex-state dot cross-point architecture. These results imply that the optimized pulse-type rotating fields in the basic cross-point-architecture are energy efficient and reliable means of selective information recording. This work is supported by Basic Science Research Program through the National Research Foundation of Korea (NRF) funded by the Ministry of Education, Science, and Technology (Grant No. 20100000706). The operation of soft X-ray microscopy measurements was supported by the Director, Office of Science, Office of Basic Energy Sciences, Materials Science and Engineering Division, of the U.S. Department of Energy.

Reference
[1]T. Shinjo et al. ., Science 289, 930(2000); A. Wachowiak et al. ., Science 298, 577(2002)
[2]B. Van. Waeyenberge et al. .,Nature 444, 461 (2006); M. Curcic et al. ., Phys. Rev. Lett. 101, 197204 (2008) ; K.-S. Lee et al. ., Phys. Rev. Lett. 101, 267206 (2008)
[3]S.–K. Kim et al. ., Appl. Phys. Lett. 92, 022509 (2008); S. –K. Kim et al. ., IEEE Trans. Mag. 44, 3071 (2008)
[4]P. Fischer at al. , Mater. Today 9, 26 (2006)
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[2010] Nonvolatile Vortex Random Access Memory

한국자기학회 2010년도 임시총회 및 하계학술연구발표회 - Invited talk

장소 : 호텔 인터불고, 원주
일정 : 2010년 6월 10일 ~ 12일
제목 : Nonvolatile Vortex Random Access Memory
발표자 : Sang-Koog Kim*, Young-Sang Yu, Ki-Suk Lee, Hyunsung Jung, Youn-Seok Choi, Jun-Young Lee, Myoung-Woo Yoo, Dong-Soo Han, Mi-Young Im and Peter Fischer

초록 :
An energy-efficient, ultrahigh-density, ultrafast, and nonvolatile solid-state universal memory is a long-held dream in the field of information-storage technology [1]. The magnetic random access memory (MRAM) [2] along with an alternative spin-transfer-torque switching mechanism [3,4] becomes a strong candidate for such a memory, owing to its nonvolatility, infinite endurance, and fast random access. The magnetic vortex having the fourfold ground state in patterned soft magnetic dots promises ground-breaking applications in information-storage devices, owing to its very stable twofold ground state of either their upward or downward core magnetization orientation [5,6] and plausible core switching by in-plane alternating magnetic fields [7] or spin-polarized currents [8]. However, low-power recording and reliable selection of each memory cell with already existing cross-point architectures have not yet been resolved for the basic operations in information storage, that is, writing (recording) and readout [9].

In this talk, we report on an experimental demonstration of magnetic vortex random access memory (VRAM) based on the cross-point architecture scheme. Reliable cell selection and low-power-consumption control of switching of out-of-plane core magnetizations have been realized using specially designed rotating magnetic fields generated by two orthogonal and unipolar Gaussian-pulse currents along with optimized pulse width and time delay. These storage and recording operations based on a medium composed of patterned vortex-state disks, together with the novel phenomenon of ultrafast vortex-core switching can stimulate further fruitful research on MRAMs that are based on vortex-state dot arrays.

This research was supported by Basic Science Research Program through the National Research Foundation of Korea (NRF) funded by the Ministry of Education, Science, and Technology (Grant No. 20090063589). The operation of the soft X-ray microscope was supported by the Director, Office of Science, Office of Basic Energy Sciences, Materials Sciences and Engineering Division, of the U.S. Department of Energy.

References:
[1] Chappert, C., Fert, A. & Van Dau, F. N. The emergence of spin electronics in data storage. Nature Mater. 6, 813 (2007).
[2] Daughton, J. M. Magnetic tunneling applied to memory. J. Appl. Phys. 81, 3758–3763 (1997).
[3] Slonczewski, J. Current-driven excitation of magnetic multilayers. J. Magn. Magn. Mater. 159, L1-L7 (1996).
[4] Berger, L. Emission of spin waves by a magnetic multilayer traversed by a current. Phys. Rev. B 54, 9353–9358 (1996).
[5] Shinjo, T. et al. Magnetic vortex core observation in circular dots of Permalloy. Science 289, 930 (2000).
[6] Wachowiak, A. et al. Direct observation of internal spin structure of magnetic vortex cores. Science 298, 577 (2002).
[7] Van Waeyenberge, B. et al. Magnetic vortex core reversal by excitation with short bursts of an alternating field. Nature 444, 461 (2006).
[8] Yamada, K. et al. Electrical switching of the vortex core in a magnetic disk. Nature Mater. 6, 269 (2007).
[9] Kim, S.-K., Lee, K.-S., Yu, Y.-S. & Choi, Y.-S. Reliable low-power control of ultrafast vortex-core switching with the selectivity in an array of vortex states by in-plane circular-rotational magnetic fields and spin-polarized currents. Appl. Phys. Lett. 92, 022509 (2008).
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[2009] IBM invited talk (host: S.S.P. Parkin)

IBM invited talk (host: S.S.P. Parkin) - Invited talk

장소 : IBM Almaden Research Center, San Francisco, USA
일정 : 2009년 10월 19일
제목 : Robust Dynamics of Magnetic Vortices in Soft Magnetic Nanodots: From Fundamental to Application
발표자 : Sang-Koog Kim
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[2009] Advanced Light Source–Moleuclar Foundry Joint Users' Meeting

Advanced Light Source–Moleuclar Foundry Joint Users' Meeting - Invited talk

장소 : Lawrence Berkeley National Lab (LBNL), Berkeley, USA
일정 : 2009년 10월 15일 ~ 17일
제목 : Vortex Dynamics in Nanoscale Magnetic Thin Films
발표자 : Sang-Koog Kim

초록 :
Since curling magnetization configurations in patterned soft magnetic dots were experimentally observed [1], the so-called magnetic vortex has been a growing interest in the fields of both nanomagnetism and spin dynamics 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 implementation in nonvolatile memory devices[11].
In this presentation, I will review several discoveries of the novel dynamic properties ofvortex-core switching from recent experimental and numerical studies, including the mechanism [4-5], the physical origin [6], and the universal criterion [7] from the fundamental perspective. I will then present the universal phase diagrams of vortex-core switching with respect to the frequency and strength of circularly rotating fields from the technological point of view [7]. Moreover, I will propose a concept of the new class of vortex random access memory (VRAM) using an array of vortex-state nanodots [8,11].
This work offers not only in-depth physical understandings of vortex dynamics, but the reliable means of information-recording and –readout using vortices.
This work was supported by Creative Research Initiatives (ReC-SDSW) of MEST.

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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