Micromagnetic Simulation of Three-dimensional Nanoarchitectures

The thesis discusses micromagnetic simulation studies on high-frequency magnetic dynamics in three-dimensional ferromagnetic nanoarchitectures made of interconnected magnetic nanowire networks. Such artificial magnetic materials with nanoscale features have recently emerged as a vivid topic of research, as their geometry has a decisive impact on their magnetic properties. By studying their static magnetization structure, we find that these systems display a behavior analogous to that of 3D artificial spin ice lattices, with frustrated interactions and the emergence of monopole-like defect structures at the wires' intersection points. Our simulations reveal a high activity of these defect sites in the magnonic high-frequency spectrum. We study various 3D nanoarchitectures and show that their geometry and magnetization state results in characteristic high-frequency signatures. Controlling these features could open new pathways for magnonics research and reprogrammable magnetic metamaterials

Magnetization dynamics in a three-dimensional interconnected nanowire array

Three-dimensional magnetic nanostructures have recently emerged as artificial magnetic material types with unique properties bearing potential for applications, including magnonic devices. Interconnected magnetic nanowires are a sub-category within this class of materials that is attracting particular interest. We investigate the high-frequency magnetization dynamics in a cubic array of cylindrical magnetic nanowires through micromagnetic simulations based on a frequency-domain formulation of the linearized Landau-Lifshitz-Gilbert equation. The small-angle high-frequency magnetization dynamics excited by an external oscillatory field displays clear resonances at distinct frequencies. These resonances are identified as oscillations connected to specific geometric features and micromagnetic configurations. The geometry- and configuration-dependence of the nanowire array's absorption spectrum demonstrates the potential of such magnetic systems for tuneable and reprogrammable magnonic applications.Comment: 7 pages, 5 figure

Interpretation of spin wave modes in Co/Ag nanodot arrays probed by broadband ferromagnetic resonance

Ferromagnetic resonance (FMR) and the measurement of magnetization dynamics in general have become sophisticated tools for the study of magnetic systems at the nanoscale. Nanosystems, such as the nanodots of this study, are technologically important structures, which find applications in a number of devices, such as magnetic storage and spintronic systems. In this work, we describe the detailed investigation of cobalt nanodots with a 200 nm diameter arranged in a square pitch array with a periodicity of 400 nm. Due to their size, such structures can support standing spin-wave modes, which can have complex spectral responses. To interpret the experimentally measured broadband FMR, we are comparing the spectra of the nanoarray structure with the unpatterned film of identical thickness. This allows us to obtain the general magnetic properties of the system, such as the magnetization, g-factor and magnetic anisotropy. We then use state-of-the-art simulations of the dynamic response to identify the nature of the excitation modes. This allows us to assess the boundary conditions for the system. We then proceed to calculate the spectral response of our system, for which we obtained good agreement. Indeed, our procedure provides a high degree of confidence, since we have interpreted all the experimental data to a good degree of accuracy. In presenting this work, we provide a full description of the theoretical framework and its application to our system, and we also describe in detail the novel simulation method used.Comment: 20 pages, 14 figure

Simulations micromagnétiques de nano-architectures tridimensionnelles

Cette thèse traite de simulations micromagnétiques de la dynamique hyperfréquence de l’aimantation dans des nano-architectures tridimensionnelles (3D) constituées de réseaux de nanofils interconnectés. Les propriétés magnétiques de tels nanomatériaux artificiels sont fortement influencées par leur géométrie. En étudiant la structure magnétique statique de ces systèmes, nous montrons des configurations correspondant à des réseaux de glace de spin artificiels 3D, avec des interactions frustrées et des structures de défaut monopolaires aux points d'intersection. Nos simulations révèlent une activité élevée de ces sites dans les excitations magnétiques de haute fréquence. Nous étudions diverses nano-architectures 3D et montrons que leur géométrie et leur structure magnétique donnent des signatures hyperfréquences caractéristiques. Le contrôle de ces caractéristiques pourrait ouvrir de nouvelles voies pour la recherche magnonique et dans le développement de métamatériaux magnétiques reprogrammables.The thesis discusses micromagnetic simulation studies on the high-frequency magnetic dynamics in three-dimensional (3D) nano-architectures made of interconnected magnetic nanowire networks. Such artificial magnetic materials with nanoscale features have recently emerged as a vivid topic of research, as their geometry has a decisive impact on their magnetic properties. By studying their static magnetization structure, we find that these systems display a behavior analogous to that of 3D artificial spin ice lattices, with frustrated interactions and the emergence of monopole-like defect structure at the wires’ intersection points. Our simulations reveal a high activity of these defect sites in the magnonic high-frequency spectrum. We study various 3D nano-architectures and show that their geometry and magnetization state results in characteristic high-frequency signatures. Controlling these features could open new pathways for magnonics research and reprogrammable magnetic metamaterial

Simulations micromagnétiques de nano-architectures tridimensionnelles

The thesis discusses micromagnetic simulation studies on the high-frequency magnetic dynamics in three-dimensional (3D) nano-architectures made of interconnected magnetic nanowire networks. Such artificial magnetic materials with nanoscale features have recently emerged as a vivid topic of research, as their geometry has a decisive impact on their magnetic properties. By studying their static magnetization structure, we find that these systems display a behavior analogous to that of 3D artificial spin ice lattices, with frustrated interactions and the emergence of monopole-like defect structure at the wires’ intersection points. Our simulations reveal a high activity of these defect sites in the magnonic high-frequency spectrum. We study various 3D nano-architectures and show that their geometry and magnetization state results in characteristic high-frequency signatures. Controlling these features could open new pathways for magnonics research and reprogrammable magnetic metamaterialsCette thèse traite de simulations micromagnétiques de la dynamique hyperfréquence de l’aimantation dans des nano-architectures tridimensionnelles (3D) constituées de réseaux de nanofils interconnectés. Les propriétés magnétiques de tels nanomatériaux artificiels sont fortement influencées par leur géométrie. En étudiant la structure magnétique statique de ces systèmes, nous montrons des configurations correspondant à des réseaux de glace de spin artificiels 3D, avec des interactions frustrées et des structures de défaut monopolaires aux points d'intersection. Nos simulations révèlent une activité élevée de ces sites dans les excitations magnétiques de haute fréquence. Nous étudions diverses nano-architectures 3D et montrons que leur géométrie et leur structure magnétique donnent des signatures hyperfréquences caractéristiques. Le contrôle de ces caractéristiques pourrait ouvrir de nouvelles voies pour la recherche magnonique et dans le développement de métamatériaux magnétiques reprogrammables

Switchable Magnetic Frustration in Buckyball Nanoarchitectures

International audienceRecent progress in nanofabrication has led to the emergence of three-dimensional magnetic nanostructures as a vibrant field of research. This includes the study of three-dimensional arrays of interconnected magnetic nanowires with tunable artificial spin-ice properties. Prominent examples of such structures are magnetic buckyball nanoarchitectures, which consist of ferromagnetic nanowires connected at vertex positions corresponding to those of a C60 molecule. These structures can be regarded as prototypes for the study of the transition from two- to three-dimensional spin-ice lattices. In spite of their significance for three-dimensional nanomagnetism, little is known about the micromagnetic properties of buckyball nanostructures. By means of finite-element micromagnetic simulations, we investigate the magnetization structures and the hysteretic properties of several sub-micron-sized magnetic buckyballs. Similar to ordinary artificial spin ice lattices, the array can be magnetized in a variety of zero-field states with vertices exhibiting different degrees of magnetic frustration. Remarkably, and unlike planar geometries, magnetically frustrated states can be reversibly created and dissolved by applying an external magnetic field. This easiness to insert and remove defect-like magnetic charges, made possible by the angle-selectivity of the field-induced switching of individual nanowires, demonstrates a potentially significant advantage of three-dimensional nanomagnetism compared to planar geometries. The control provided by the ability to switch between ice-rule obeying and magnetically frustrated structures could be an important feature of future applications, including magnonic devices exploiting differences in the fundamental frequencies of these configurations