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168 results on '"Kim, Joo-Von"'

162. Propagation of magnetic vortices using nanocontacts as tunable attractors.

Author

Manfrini, M., Kim, Joo-Von, Petit-Watelot, S., Van Roy, W., Lagae, L., Chappert, C., and Devolder, T.

Subjects
*SPHEROMAKS, *NANOCONTACTS, *NANOSTRUCTURED material manufacturing, *ATTRACTORS (Mathematics), *MAGNETIC properties of thin films, *GROUND state (Quantum mechanics)
Abstract

Magnetic vortices in thin films are in-plane spiral spin configurations with a core in which the magnetization twists out of the film plane. Vortices result from the competition between atomic-scale exchange forces and long-range dipolar interactions. They are often the ground state of magnetic dots, and have applications in medicine, microwave generation and information storage. The compact nature of the vortex core, which is 10-20 nm wide, makes it a suitable probe of magnetism at the nanoscale. However, thus far the positioning of a vortex has been possible only in confined structures, which prevents its transport over large distances. Here we show that vortices can be propagated in an unconstrained system that comprises electrical nanocontacts (NCs). The NCs are used as tunable vortex attractors in a manner that resembles the propelling of space craft with gravitational slingshots. By passing current from the NCs to a ferromagnetic film, circulating magnetic fields are generated, which nucleate the vortex and create a potential well for it. The current becomes spin polarized in the film, and thereby drives the vortex into gyration through spin-transfer torques. The vortex can be guided from one NC to another by tuning attractive strengths of the NCs. We anticipate that NC networks may be used as multiterminal sources of vortices and spin waves (as well as heat, spin and charge flows) to sense the fundamental interactions between physical objects and fluxes of the next-generation spintronic devices. [ABSTRACT FROM AUTHOR]

Published
2014
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164. Metal spintronics: Electronics free of charge.

Author

Chappert, Claude and Kim, Joo-Von

Subjects
*NANOTECHNOLOGY, *SPINTRONICS, *ELECTRIC currents, *SPIN valves, *MAGNETIC circuits
Abstract

The article provides information on the efforts of physicists to discover a device that will use only flow of spins. It highlights the research of Tao Yang and colleagues on how to switch magnetization of a particle from electric current to a pure spin current through the demonstration of non-local spin valve. It notes that there are many problems that need to be mastered before a free current tool will be realized.

Published
2008
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165. Damping of CoxFe80-xB20 ultrathin films with perpendicular magnetic anisotropy.

Author

Devolder, T., Ducrot, P.-H., Adam, J.-P., Barisic, I., Vernier, N., Kim, Joo-Von, Ockert, B., and Ravelosona, D.

Subjects
DAMPING (Mechanics), ANISOTROPY, MAGNETIC resonance, METALLIC composites, WAVES (Physics)
Abstract

We use vector network analyzer ferromagnetic resonance to study the perpendicularly magnetized CoFeB films. We report the dependence of the anisotropy, the g-factor, and the damping upon the Fe-Co compositional ratio in the amorphous and crystalline states. The damping and the anisotropy increase upon crystallization but vary little with composition on the Fe-rich side. At high cobalt content, the anisotropy lowers while the damping and the sample inhomogeneity increase. The compositional dependences seem to extrapolate from the properties of bulk CoFe alloys, with differences that can be understood from the correlated impacts of spin-orbit interaction on anisotropy, g-factor, and damping. [ABSTRACT FROM AUTHOR]

Published
2013
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166. Quantifying the thermal stability in perpendicularly magnetized ferromagnetic nanodisks with forward flux sampling

Author

Joo-Von Kim, Louise Desplat, Centre de Nanosciences et de Nanotechnologies (C2N), Université Paris-Saclay-Centre National de la Recherche Scientifique (CNRS), Institut de Physique et Chimie des Matériaux de Strasbourg (IPCMS), Université de Strasbourg (UNISTRA)-Matériaux et nanosciences d'Alsace (FMNGE), Institut de Chimie du CNRS (INC)-Université de Strasbourg (UNISTRA)-Université de Haute-Alsace (UHA) Mulhouse - Colmar (Université de Haute-Alsace (UHA))-Institut National de la Santé et de la Recherche Médicale (INSERM)-Centre National de la Recherche Scientifique (CNRS)-Institut de Chimie du CNRS (INC)-Université de Strasbourg (UNISTRA)-Université de Haute-Alsace (UHA) Mulhouse - Colmar (Université de Haute-Alsace (UHA))-Institut National de la Santé et de la Recherche Médicale (INSERM)-Centre National de la Recherche Scientifique (CNRS)-Centre National de la Recherche Scientifique (CNRS)-Réseau nanophotonique et optique, Centre National de la Recherche Scientifique (CNRS)-Université de Strasbourg (UNISTRA)-Université de Haute-Alsace (UHA) Mulhouse - Colmar (Université de Haute-Alsace (UHA))-Centre National de la Recherche Scientifique (CNRS)-Université de Strasbourg (UNISTRA), ANR-17-CE24-0025,TOPSKY,Propriétés topologiques des skyrmions magnétiques et opportunitiés pour le dévelopement de nouveaux dispositifs spintroniques(2017), Université de Strasbourg (UNISTRA)-Centre National de la Recherche Scientifique (CNRS)-Matériaux et Nanosciences Grand-Est (MNGE), Université de Strasbourg (UNISTRA)-Université de Haute-Alsace (UHA) Mulhouse - Colmar (Université de Haute-Alsace (UHA))-Institut National de la Santé et de la Recherche Médicale (INSERM)-Institut de Chimie du CNRS (INC)-Centre National de la Recherche Scientifique (CNRS)-Université de Strasbourg (UNISTRA)-Université de Haute-Alsace (UHA) Mulhouse - Colmar (Université de Haute-Alsace (UHA))-Institut National de la Santé et de la Recherche Médicale (INSERM)-Institut de Chimie du CNRS (INC)-Centre National de la Recherche Scientifique (CNRS)-Réseau nanophotonique et optique, Université de Strasbourg (UNISTRA)-Université de Haute-Alsace (UHA) Mulhouse - Colmar (Université de Haute-Alsace (UHA))-Centre National de la Recherche Scientifique (CNRS)-Université de Strasbourg (UNISTRA)-Centre National de la Recherche Scientifique (CNRS), Kim, Joo-Von, and Propriétés topologiques des skyrmions magnétiques et opportunitiés pour le dévelopement de nouveaux dispositifs spintroniques - - TOPSKY2017 - ANR-17-CE24-0025 - AAPG2017 - VALID

Subjects
Materials science, Nucleation, General Physics and Astronomy, Flux, FOS: Physical sciences, 02 engineering and technology, 01 natural sciences, 0103 physical sciences, Mesoscale and Nanoscale Physics (cond-mat.mes-hall), Perpendicular, Thermal stability, [NLIN] Nonlinear Sciences [physics], [NLIN]Nonlinear Sciences [physics], [PHYS.COND]Physics [physics]/Condensed Matter [cond-mat], 010306 general physics, Condensed Matter - Statistical Mechanics, ComputingMilieux_MISCELLANEOUS, [PHYS.COND.CM-MSQHE]Physics [physics]/Condensed Matter [cond-mat]/Mesoscopic Systems and Quantum Hall Effect [cond-mat.mes-hall], Magnetization dynamics, Condensed matter physics, Condensed Matter - Mesoscale and Nanoscale Physics, Statistical Mechanics (cond-mat.stat-mech), Sampling (statistics), 021001 nanoscience & nanotechnology, [PHYS.COND.CM-MS] Physics [physics]/Condensed Matter [cond-mat]/Materials Science [cond-mat.mtrl-sci], [PHYS.COND.CM-MSQHE] Physics [physics]/Condensed Matter [cond-mat]/Mesoscopic Systems and Quantum Hall Effect [cond-mat.mes-hall], Ferromagnetism, Orders of magnitude (time), 13. Climate action, [PHYS.COND.CM-MS]Physics [physics]/Condensed Matter [cond-mat]/Materials Science [cond-mat.mtrl-sci], 0210 nano-technology, [PHYS.COND] Physics [physics]/Condensed Matter [cond-mat]
Abstract

The thermal stability in nanostructured magnetic systems is an important issue for applications in information storage. From a theoretical and simulation perspective, an accurate prediction of thermally-activated transitions is a challenging problem because desired retention times are on the order of 10 years, while the characteristic time scale for precessional magnetization dynamics is of the order of nanoseconds. Here, we present a theoretical study of the thermal stability of magnetic elements in the form of perpendicularly-magnetized ferromagnetic disks using the forward flux sampling method, which is useful for simulating rare events. We demonstrate how rates of thermally-activated switching between the two uniformly-magnetized ``up'' and ``down'' states, which occurs through domain wall nucleation and propagation, vary with the interfacial Dzyaloshinskii-Moriya interaction, which affect the energy barrier separating these states. Moreover, we find that the average lifetimes differ by several orders of magnitude from estimates based on the commonly assumed value of 1 GHz for the attempt frequency., Comment: 10 pages, 9 figures

Published
2020
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167. Entropy-reduced retention times in magnetic memory elements: A case of the Meyer-Neldel Compensation Rule

Author

Joo-Von Kim, Louise Desplat, Centre de Nanosciences et de Nanotechnologies (C2N), Université Paris-Saclay-Centre National de la Recherche Scientifique (CNRS), Institut de Physique et Chimie des Matériaux de Strasbourg (IPCMS), Université de Strasbourg (UNISTRA)-Matériaux et nanosciences d'Alsace (FMNGE), Institut de Chimie du CNRS (INC)-Université de Strasbourg (UNISTRA)-Université de Haute-Alsace (UHA) Mulhouse - Colmar (Université de Haute-Alsace (UHA))-Institut National de la Santé et de la Recherche Médicale (INSERM)-Centre National de la Recherche Scientifique (CNRS)-Institut de Chimie du CNRS (INC)-Université de Strasbourg (UNISTRA)-Université de Haute-Alsace (UHA) Mulhouse - Colmar (Université de Haute-Alsace (UHA))-Institut National de la Santé et de la Recherche Médicale (INSERM)-Centre National de la Recherche Scientifique (CNRS)-Centre National de la Recherche Scientifique (CNRS)-Réseau nanophotonique et optique, Centre National de la Recherche Scientifique (CNRS)-Université de Strasbourg (UNISTRA)-Université de Haute-Alsace (UHA) Mulhouse - Colmar (Université de Haute-Alsace (UHA))-Centre National de la Recherche Scientifique (CNRS)-Université de Strasbourg (UNISTRA), ANR-17-CE24-0025,TOPSKY,Propriétés topologiques des skyrmions magnétiques et opportunitiés pour le dévelopement de nouveaux dispositifs spintroniques(2017), Kim, Joo-Von, Propriétés topologiques des skyrmions magnétiques et opportunitiés pour le dévelopement de nouveaux dispositifs spintroniques - - TOPSKY2017 - ANR-17-CE24-0025 - AAPG2017 - VALID, Université de Strasbourg (UNISTRA)-Centre National de la Recherche Scientifique (CNRS)-Matériaux et Nanosciences Grand-Est (MNGE), Université de Strasbourg (UNISTRA)-Université de Haute-Alsace (UHA) Mulhouse - Colmar (Université de Haute-Alsace (UHA))-Institut National de la Santé et de la Recherche Médicale (INSERM)-Institut de Chimie du CNRS (INC)-Centre National de la Recherche Scientifique (CNRS)-Université de Strasbourg (UNISTRA)-Université de Haute-Alsace (UHA) Mulhouse - Colmar (Université de Haute-Alsace (UHA))-Institut National de la Santé et de la Recherche Médicale (INSERM)-Institut de Chimie du CNRS (INC)-Centre National de la Recherche Scientifique (CNRS)-Réseau nanophotonique et optique, and Université de Strasbourg (UNISTRA)-Université de Haute-Alsace (UHA) Mulhouse - Colmar (Université de Haute-Alsace (UHA))-Centre National de la Recherche Scientifique (CNRS)-Université de Strasbourg (UNISTRA)-Centre National de la Recherche Scientifique (CNRS)

Subjects
Waiting time, General Physics and Astronomy, FOS: Physical sciences, 02 engineering and technology, Activation energy, 01 natural sciences, law.invention, Magnetization, symbols.namesake, law, 0103 physical sciences, Mesoscale and Nanoscale Physics (cond-mat.mes-hall), Magnetic memory, [NLIN] Nonlinear Sciences [physics], [NLIN]Nonlinear Sciences [physics], [PHYS.COND]Physics [physics]/Condensed Matter [cond-mat], 010306 general physics, Condensed Matter - Statistical Mechanics, ComputingMilieux_MISCELLANEOUS, [PHYS.COND.CM-MSQHE]Physics [physics]/Condensed Matter [cond-mat]/Mesoscopic Systems and Quantum Hall Effect [cond-mat.mes-hall], Physics, Arrhenius equation, Condensed Matter - Mesoscale and Nanoscale Physics, Condensed matter physics, Statistical Mechanics (cond-mat.stat-mech), Magnetic storage, 021001 nanoscience & nanotechnology, [PHYS.COND.CM-MS] Physics [physics]/Condensed Matter [cond-mat]/Materials Science [cond-mat.mtrl-sci], Exponential function, [PHYS.COND.CM-MSQHE] Physics [physics]/Condensed Matter [cond-mat]/Mesoscopic Systems and Quantum Hall Effect [cond-mat.mes-hall], [PHYS.COND.CM-MS]Physics [physics]/Condensed Matter [cond-mat]/Materials Science [cond-mat.mtrl-sci], symbols, 0210 nano-technology, [PHYS.COND] Physics [physics]/Condensed Matter [cond-mat]
Abstract

We compute mean waiting times between thermally-activated magnetization reversals in a nanodisk with parameters similar to a free CoFeB layer used in magnetic random access memories. By combining Langer's theory and forward flux sampling simulations, we show that the Arrhenius prefactor can take values up to 10$^{21}$ Hz, orders of magnitude beyond the value of 10$^{9}$ Hz typically assumed, and varies drastically as a function of material parameters. We show that the prefactor behaves like an exponential of the activation energy, which highlights a case of the Meyer-Neldel compensation rule. This suggests that modeling information retention times with a barrier-independent prefactor in such magnetic storage elements is not justified., Comment: 5 pages, 4 figures

Published
2020
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168. Domain-wall motion and interfacial Dzyaloshinskii-Moriya interactions in Pt/Co/Ir( t Ir )/Ta multilayers.

Author

Shahbazi K, Kim JV, Nembach HT, Shaw JM, Bischof A, Rossell MD, Jeudy V, Moore TA, and Marrows CH

Abstract

The interfacial Dzyaloshinskii-Moriya interaction (DMI) is important for chiral domain walls (DWs) and for stabilizing magnetic skyrmions. We study the effects of introducing increasing thicknesses of Ir, from zero to 2 nm, into a Pt/Co/Ta multilayer between the Co and Ta layers. There is a marked increase in magnetic moment, due to the suppression of the dead layer at the interface with Ta, but the perpendicular anisotropy is hardly affected. All samples show a universal scaling of the field-driven DW velocity across the creep and depinning regimes. Asymmetric bubble expansion shows that DWs in all of the samples have the left-handed Néel form. The value of in-plane magnetic field at which the creep velocity shows a minimum drops markedly on the introduction of Ir, as does the frequency shift of the Stokes and anti-Stokes peaks in Brillouin light scattering (BLS) measurements. Despite this qualitative similarity, there are quantitative differences in the DMI strength given by the two measurements, with BLS often returning higher values. Many features in bubble expansion velocity curves do not fit simple models commonly used, namely a lack of symmetry about the velocity minimum and no difference in velocities at high in-plane fields. These features are explained by the use of a new model in which the depinning field is allowed to vary with in-plane field in a way determined from micromagnetic simulations. This theory shows that the velocity minimum underestimates the DMI field, consistent with BLS giving higher values. Our results suggest that the DMI at an Ir/Co interface has the same sign as the DMI at a Pt/Co interface.

Published
2019
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