Article
Mechanics
S. J. Terrington, K. Hourigan, M. C. Thompson
Summary: This article presents a three-dimensional theory of vorticity creation on generalised interfaces, including both non-slip and free-slip boundaries. Vorticity can be created on a boundary by the inviscid relative acceleration between fluid elements on each side of the boundary, driven by either tangential pressure gradients or body forces. Viscosity acts to transfer circulation between the vortex sheet representing the slip velocity on the interface, and the fluid interior, but is not responsible for the creation of vorticity on the interface. This formulation also describes a principle of vorticity conservation for interfacial and free-surface flows.
JOURNAL OF FLUID MECHANICS
(2022)
Article
Mechanics
S. J. Terrington, K. Hourigan, M. C. Thompson
Summary: Lyman's proposed definition of the boundary vorticity flux offers conceptual benefits in describing the transfer of circulation across a boundary, extending to three-dimensional flows, and enabling control-surface analysis. The definition also illustrates how the kinematic condition of vortex lines not ending in the fluid is maintained, providing an elegant description of viscous processes like vortex reconnection. The examination of flow over a sphere using Lyman's definition demonstrates the benefits of the proposed framework in understanding vortical flow dynamics.
JOURNAL OF FLUID MECHANICS
(2021)
Article
Mechanics
G. A. M. van Kuik
Summary: This article introduces the significance of Prandtl's force field method in modern wind energy research and classifies and analyzes which type of body force field generates vorticity and converts energy. In addition, by re-deriving the Kutta-Joukowsky load and the relation between bound and trailing vorticity of a wing, it confirms the consistency between the force field method and the load output analysis method.
JOURNAL OF FLUID MECHANICS
(2022)
Article
Chemistry, Multidisciplinary
Olivier Noel, Pierre-Emmanuel Mazeran, Igor Stankovic
Summary: This paper investigates the physics of dynamic friction on water molecule contaminated surfaces, focusing on friction mechanisms in hydrophobic contact. Experimental investigations and molecular dynamic simulations reveal that water molecules form droplets within the sliding nanocontact instead of being squeezed out, leading to a full slip regime on the hydrophobic substrate. This research is of great significance for understanding the dynamic friction behavior of water molecules on surfaces.
Article
Chemistry, Multidisciplinary
Lukas Powalla, Max T. Birch, Kai Litzius, Sebastian Wintz, Frank Schulz, Markus Weigand, Tanja Scholz, Bettina Lotsch, Klaus Kern, Gisela Schuetz, Marko Burghard
Summary: Skyrmions, potential particles with practical applications, have been observed in chiral magnets and magnetic thin films. Recently, monochiral skyrmions have been found in two-dimensional van der Waals magnets, offering new prospects for skyrmion applications. However, controlling the nucleation of skyrmions within these materials remains a challenge.
Article
Mechanics
Dmitriy Zhigunov, Roman O. Grigoriev
Summary: This paper presents new classes of unstable recurrent solutions of the two-dimensional Euler equation with periodic boundary conditions. These solutions resemble the recurrent solutions of the Navier-Stokes equation, known as exact coherent structures. The Euler equation solutions come in infinite-dimensional continuous families, are connected to different types of solutions, and exhibit weak instability, leading to the frequent occurrence of these solutions in fully developed turbulence.
JOURNAL OF FLUID MECHANICS
(2023)
Review
Engineering, Civil
Khay-Wai Leong, Michael MacDonald, John E. Cater, Richard G. J. Flay
Summary: This article discusses the behavior of buoyancy-induced vortex flow and its potential for harnessing kinetic energy for electricity production. A large heat flux over a large surface area is needed to create and maintain a vortex. A single-cell vortex has the highest energy flux to circulation strength ratio, but a two-cell vortex, although having higher tangential velocity, is less stable.
JOURNAL OF WIND ENGINEERING AND INDUSTRIAL AERODYNAMICS
(2022)
Article
Mechanics
David Deepwell, Cameron Clarry, Christopher Subich, Marek Stastna
Summary: Internal solitary waves passing through a narrow channel with isolated sidewalls induce vortices which result in horizontal tracer exchange and vertical transport, with the height of the transport being proportional to the square of the vertical vorticity. Increasing wave amplitude leads to stronger vortices and enhanced transport. The three-dimensional nature of the instability in the sidewall case sets it apart from typical instabilities caused by internal solitary waves.
JOURNAL OF FLUID MECHANICS
(2021)
Article
Mechanics
Josh Shelton, Philippe H. H. Trinh
Summary: There has been significant interest in studying water waves coupled with non-zero vorticity. In this study, we derive analytical approximations for free-surface waves generated by submerged point vortices at low Froude numbers. Our findings show that the presence of Stokes lines originating from a vortex leads to the formation of waves. Trapped waves can occur when multiple point vortices are present, and this phenomenon is observed for a countably infinite set of Froude numbers in the two-vortex problem.
JOURNAL OF FLUID MECHANICS
(2023)
Article
Mechanics
T. W. Christopher, Stefan G. Llewellyn Smith
Summary: Equilibrium solutions for hollow vortices in straining flow in a corner are obtained by solving a free-boundary problem. The solutions depend on the corner angle and on the non-dimensional ratio of strain to circulation, resulting in a two-parameter family of solutions.
JOURNAL OF FLUID MECHANICS
(2021)
Article
Mechanics
D. I. Pullin, John E. Sader
Summary: The study focuses on the trailing-edge vortex produced by the start-up motion of a two-dimensional flat plate in an inviscid fluid. A vortex-sheet representation and power-law similarity solution are developed, leading to the discovery of three distinct start-up vortex-structure types. The properties of each type are detailed for special cases, with discussion on numerical and analytical solutions. In addition, singular and degenerate vortex behavior is discovered, and the transition between solution types is examined.
JOURNAL OF FLUID MECHANICS
(2021)
Article
Mechanics
R. B. Nelson, V. S. Krishnamurthy, D. G. Crowdy
Summary: This study examines the shapes and properties of two steadily rotating, equal circulation, two-dimensional hollow vortices, finding a one-parameter family of solutions and comparing the results to a previous study on uniform vorticity patches. It is observed that although the general behavior of the two systems is similar, there are some differences highlighted, especially when the vortices become close to touching.
JOURNAL OF FLUID MECHANICS
(2021)
Article
Engineering, Aerospace
Dominic Schroeder, Thomas Leweke, Ralf Hoernschemeyer, Eike Stumpf
Summary: This study investigates the flow characteristics of the wake behind a rectangular wing using both experimental and numerical methods. By modifying the wingtip geometry with the addition of a perpendicular fin, two closely-spaced tip vortices are generated to reduce the impact of vortices. Velocity measurements were conducted in the near wake of the wing to determine the characteristics of the tip vortex pair, and different configurations of the fin were tested. The results show that a strong and concentrated secondary vortex can only be generated when the fin is placed on the pressure side of the wing. Visualizations and numerical simulations were used to analyze the influence of fin parameter variations on the tip vortex pair.
AEROSPACE SCIENCE AND TECHNOLOGY
(2022)
Article
Mechanics
Seyedmohammad Mousavisani, Naumi Noshin Chowdhury, Hadi Samsam-Khayani, Hamed Samandari, Banafsheh Seyed-Aghazadeh
Summary: This study experimentally investigated the vortex-induced vibration (VIV) of a two degree-of-freedom (DOF) circular cylinder in a recirculating water tunnel. Different vibration modes and vortex structures were observed within a certain velocity range.
JOURNAL OF FLUID MECHANICS
(2022)
Article
Nanoscience & Nanotechnology
Di Lin, Yutong Feng, Zhengqi Ren, David J. Richardson
Summary: Efficient generation of high-peak-power femtosecond optical vortex pulses with selectable topological charge has been successfully demonstrated from a fiber oscillator using a few-mode polarization-maintaining ytterbium-doped fiber. This unprecedented performance level is of great interest for applications such as materials processing and imaging.
Article
Physics, Applied
Paul Bouquin, Joo-Von Kim, Olivier Bultynck, Siddharth Rao, Sebastien Couet, Gouri Sankar Kar, Thibaut Devolder
Summary: In sub-100-nm-diameter magnetic tunnel junctions, magnetization reversal through domain-wall motion is shown to be dominated by two distinct stochastic effects: incubation delay related to domain-wall nucleation and stochastic motion in the Walker regime. Micromagnetics simulations reveal various factors contributing to temporal pinning of the wall near the disk center, such as vertical-Bloch line nucleation and wall precession. Reproducible ballistic motion is achieved when the Bloch and Neel wall profiles become degenerate in energy in optimally sized disks, enabling quasideterministic motion.
PHYSICAL REVIEW APPLIED
(2021)
Article
Physics, Applied
Jerome Williame, Joo-Von Kim
Summary: In this study, a time-delay oscillator using Mackey-Glass nonlinearity based on a pinned magnetic domain wall in a thin film nanostrip is proposed. By applying electric currents along the strip, the domain wall is deformed and displaced through spin transfer torques, which can be converted into a nonlinear transfer function. Micromagnetics simulations are used to investigate the effects of readout position, time delay, and feedback gain on the dynamics of the domain wall, highlighting the potential for self-sustained oscillations and complex transients.
APPLIED PHYSICS LETTERS
(2021)
Article
Physics, Applied
Zhiyang Zeng, Zhaochu Luo, Laura J. Heyderman, Joo-Von Kim, Ales Hrabec
Summary: The study introduces a spintronic oscillator based on chiral coupling in thin magnetic films and demonstrates its potential application in neuromorphic computing through experiments.
APPLIED PHYSICS LETTERS
(2021)
Review
Nanoscience & Nanotechnology
Felix Trier, Paul Noel, Joo-Von Kim, Jean-Philippe Attane, Laurent Vila, Manuel Bibes
Summary: Oxide materials exhibit a wide range of functional properties, where electron correlations and spin-orbit coupling play significant roles. Recent advances in oxide spin-orbitronics have led to the realization of exotic phenomena and new functionalities for spintronics applications. The future prospects for this field involve further exploration of spin-charge interconversion, topological spin textures, and the influence of ferroelectricity on spin-orbit-driven effects.
NATURE REVIEWS MATERIALS
(2022)
Article
Physics, Applied
Jean-Lois Bello, Yassine Quessab, Jun-Wen Xu, Maxime Verges, Heloise Damas, Sebastien Petit-Watelot, Juan-Carlos Rojas Sanchez, Michel Hehn, Andrew D. Kent, Stephane Mangin
Summary: In this study, the switching of magnetization in Ir/GdFeCo/Cu/Pt heterostructures is observed at zero applied magnetic field, which is shown to be a result of the competition between spin-orbit torque, the Oersted field generated by the charge current, and the coercivity of the material. This finding provides a new approach for the design of future spintronics devices.
JOURNAL OF APPLIED PHYSICS
(2022)
Article
Multidisciplinary Sciences
Matthieu Grelier, Florian Godel, Aymeric Vecchiola, Sophie Collin, Karim Bouzehouane, Albert Fert, Vincent Cros, Nicolas Reyren
Summary: Three-dimensional spin textures, including skyrmion cocoons, have been observed in aperiodic multilayers and can coexist with standard tube-like skyrmions. These novel textures have potential technological applications and can be electrically detected using magneto-transport measurements.
NATURE COMMUNICATIONS
(2022)
Article
Nanoscience & Nanotechnology
Titiksha Srivastava, Yanis Sassi, Fernando Ajejas, Aymeric Vecchiola, Igor Ngouagnia Yemeli, Herve Hurdequint, Karim Bouzehouane, Nicolas Reyren, Vincent Cros, Thibaut Devolder, Joo-Von Kim, Gregoire de Loubens
Summary: This study combines magnetic force microscopy, broadband ferromagnetic resonance, and micromagnetics simulations to show that a high-frequency mode accompanies the skyrmion lattice phase in thin-film multilayers of [Pt/FeCoB/AlOx](20). This mode involves the precession of skyrmion cores, generating 50-80 nm wavelength spin waves in the uniformly magnetized background. The observations are made possible by a low Gilbert damping constant, which is almost an order of magnitude lower than in similar ultrathin materials. The simulations also reveal the complex three-dimensional spin structure of the skyrmion cores, which plays a crucial role in spin wave generation.
Article
Materials Science, Multidisciplinary
A. Mouhoub, F. Millo, C. Chappert, J- Kim, J. Letang, A. Solignac, T. Devolder
Summary: We developed a reliable method to quantify the interlayer exchange coupling and intralayer exchange stiffness in synthetic antiferromagnets, and applied it to a specific material platform. We found that the interplay between the two exchange interactions leads to a gradient of magnetization orientation across the stack, which nontrivially affects its hysteresis and spin wave eigenmodes. Using micromagnetic simulations and experimental measurements, we determined the magnetic parameters that best describe the sample behavior, revealing the independence of exchange stiffness on thickness and the variation of interlayer exchange coupling with thickness.
PHYSICAL REVIEW MATERIALS
(2023)
Article
Multidisciplinary Sciences
Lukas Koerber, Christopher Heins, Tobias Hula, Joo-Von Kim, Sonia Thlang, Helmut Schultheiss, Juergen Fassbender, Katrin Schultheiss
Summary: Magnons are elementary excitations in magnetic materials that can undergo nonlinear multimode scattering processes. By harnessing the interaction between magnon modes, pattern recognition can be achieved. Experimental results show that different azimuthal modes can be excited through three-magnon scattering, with amplitude dependent on the input sequences. Recognition rates as high as 99.4% can be achieved for four-symbol sequences using scattered modes, even in the presence of amplitude noise.
NATURE COMMUNICATIONS
(2023)
Article
Materials Science, Multidisciplinary
K. Ait Oukaci, D. Stoeffler, M. Hehn, M. Grassi, B. Sarpi, M. Bailleul, Y. Henry, S. Petit, F. Montaigne, R. Belkhou, D. Lacour
Summary: By combining volume sensitive high resolution Magnetic Force Microscopy with surface sensitive X-ray Photoemission Electron Microscopy, the depth profile of a weak stripe magnetic texture and its evolution upon in-plane magnetization reversal were resolved. It was shown that the conventional weak stripe texture undergoes a well-defined undulation while the magnetic field is reversed to negative after in plane positive saturation. This reversal mode is characterized by a checker board pattern of alternating surface magnetic charges and by a longitudinal modulation of the in-plane component of magnetization.
MATERIALS RESEARCH LETTERS
(2023)
Article
Materials Science, Multidisciplinary
V. Palin, A. Anadon, S. Andrieu, Y. Fagot-Revurat, C. de Melo, J. Ghanbaja, O. Kurnosikov, S. Petit-Watelot, F. Bertran, J. -c. Rojas-Sanchez
Summary: This study explores a promising family of topological materials called half-Heuslers, which have high tunability and large spin Seebeck coefficient. The research findings provide a new pathway for the development of efficient spin interconversion materials.
PHYSICAL REVIEW MATERIALS
(2023)
Article
Chemistry, Multidisciplinary
Adrian Benedit-Cardenas, Stephanie Bruyere, Sylvie Migot, Thomas Hauet, Sebastien Petit-Watelot, Pascal Boulet, Dominique Muller, Dmitry A. Zuev, David Horwat, Alexandre Nomine
Summary: Green and digital transitions will create high demand for metals and semiconductors, raising concerns about material availability. Addressing this challenge requires the discovery of sustainable materials and expanding their functionalities. By controlling out-of-stable equilibrium processes, researchers achieved precise control over the crystallization of non-stoichiometric MnSix and discovered that metastability could enhance material properties.
MATERIALS HORIZONS
(2023)
Article
Materials Science, Multidisciplinary
T. Devolder, S-M Ngom, A. Mouhoub, J. Letang, J- Kim, P. Crozat, J-P Adam, A. Solignac, C. Chappert
Summary: We studied how to characterize a population of spin waves by analyzing the electrical microwave noise. The noise contains contributions from both incoherent spin waves and electronic fluctuations. By separating these contributions, we can obtain information about the magnetic susceptibility and the mode-resolved effective magnon temperature.
Article
Materials Science, Multidisciplinary
Jeremy Letang, Claudia de Melo, Charles Guillemard, Aymeric Vecchiola, Damien Rontani, Sebastien Petit-Watelot, Myoung-Woo Yoo, Thibaut Devolder, Karim Bouzehouane, Vincent Cros, Stephane Andrieu, Joo-Von Kim
Summary: This experimental study focuses on the vortex dynamics in magnetic nanocontacts based on pseudo spin valves comprising the Co2MnGe Heusler compound. By combining precise film growth and nanoindentation techniques, different types of spin-transfer induced dynamics related to different modes of the magnetic vortex configuration were observed, such as mode hopping, mode coexistence, and mode extinction, in addition to the usual gyration mode.
