subject:(Micromagnetic modelling)

University of Exeter

1. Whitehead, N. Making the grade : generating & controlling spin waves with a graded refractive index.

Degree: PhD, 2020, University of Exeter

► In this thesis, the magnetic parameters of a ferromagnetic film are varied to create refractive index profiles for spin waves. The properties of this "magnonic"… (more)

▼ In this thesis, the magnetic parameters of a ferromagnetic film are varied to create refractive index profiles for spin waves. The properties of this "magnonic" refractive index are studied for different frequency regimes. Analytical theory and numerical modelling are used throughout. The research in this work is along two main themes. The first involves the generation of spin waves from a graded (or stepped) refractive index region. The energy is driven into the system via a harmonic yet spatially-uniform external magnetic field, and it is shown that the graded index feature may then act as a spin wave source. Exchange (short wavelength) spin waves are studied in this case, since their dynamics are described by the Landau-Lifshitz equation that can be linearised to form a Schrödinger-like equation. This exchange regime is therefore ideal for exploring how the features of well-known exactly-solvable models manifest themselves for spin waves. The exactly-solvable models in this case are a square potential barrier and a Pöschl-Teller potential well. The latter naturally occurs as a magnetic domain wall in a ferromagnet, with a fixed potential 'height'. Spin waves can be generated by both features, but spin wave emission is not guaranteed. The excitation frequency must primarily be above a threshold value, akin to the 'work function' energy in quantum mechanics. Furthermore, certain heights of the potential (or frequencies of excitation) can lead to confinement within the potential region. The second theme studied in this work involves using a graded refractive index to focus or steer spin waves. The rotationally-symmetric graded index lenses, well known in optics, are realised here for spin waves in a perpendicularly- magnetised film, for magnetostatic (long wavelength) spin waves. In this regime, the magnetisation only needs to be changed by a tiny amount, of the order of 2%, to create a Luneburg lens. For the steering lenses, which require a singular refractive index in the centre, just a 10% increase in the magnetisation can create the steering lenses almost exactly. The general properties of the magnonic refractive index are also analysed, for the entire range of spin wave wavelengths, from millimetres to nanometres. The magnetostatic regime is found to be ideal for creating extreme changes in the refractive index, theoretically from 1 to over 100.

Subjects/Keywords: 500; spin waves; micromagnetic modelling; analytical theory

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APA (6^th Edition):

Whitehead, N. (2020). Making the grade : generating & controlling spin waves with a graded refractive index. (Doctoral Dissertation). University of Exeter. Retrieved from http://hdl.handle.net/10871/40600

Chicago Manual of Style (16^th Edition):

Whitehead, N. “Making the grade : generating & controlling spin waves with a graded refractive index.” 2020. Doctoral Dissertation, University of Exeter. Accessed March 03, 2021. http://hdl.handle.net/10871/40600.

MLA Handbook (7^th Edition):

Whitehead, N. “Making the grade : generating & controlling spin waves with a graded refractive index.” 2020. Web. 03 Mar 2021.

Vancouver:

Whitehead N. Making the grade : generating & controlling spin waves with a graded refractive index. [Internet] [Doctoral dissertation]. University of Exeter; 2020. [cited 2021 Mar 03]. Available from: http://hdl.handle.net/10871/40600.

Council of Science Editors:

Whitehead N. Making the grade : generating & controlling spin waves with a graded refractive index. [Doctoral Dissertation]. University of Exeter; 2020. Available from: http://hdl.handle.net/10871/40600

University of Edinburgh

2. Barron, Louise Lillias Margaret. Effect of exchange and magnetostatic interactions on grain boundaries.

Degree: PhD, 2011, University of Edinburgh

URL: http://hdl.handle.net/1842/5023

► Magnetic minerals are abundant within our Earth's crust and can retain, through one of a number of processes, a remanent magnetisation induced by the Earth's… (more)

Subjects/Keywords: 550; micromagnetic modelling; palaeomagnetism; rock magnetism

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APA (6^th Edition):

Barron, L. L. M. (2011). Effect of exchange and magnetostatic interactions on grain boundaries. (Doctoral Dissertation). University of Edinburgh. Retrieved from http://hdl.handle.net/1842/5023

Chicago Manual of Style (16^th Edition):

Barron, Louise Lillias Margaret. “Effect of exchange and magnetostatic interactions on grain boundaries.” 2011. Doctoral Dissertation, University of Edinburgh. Accessed March 03, 2021. http://hdl.handle.net/1842/5023.

MLA Handbook (7^th Edition):

Barron, Louise Lillias Margaret. “Effect of exchange and magnetostatic interactions on grain boundaries.” 2011. Web. 03 Mar 2021.

Vancouver:

Barron LLM. Effect of exchange and magnetostatic interactions on grain boundaries. [Internet] [Doctoral dissertation]. University of Edinburgh; 2011. [cited 2021 Mar 03]. Available from: http://hdl.handle.net/1842/5023.

Council of Science Editors:

Barron LLM. Effect of exchange and magnetostatic interactions on grain boundaries. [Doctoral Dissertation]. University of Edinburgh; 2011. Available from: http://hdl.handle.net/1842/5023

3. Trapp, Beatrix. Nucleation and propagation of magnetic domain walls in cylindrical nanowires with diameter modulations : Nucléation et propagation de parois de domaine magnétiques dans des nanofils cylindriques avec des modulations en diamètre.

Degree: Docteur es, Nanophysique, 2018, Université Grenoble Alpes (ComUE)

URL: http://www.theses.fr/2018GREAY011

► Dans les dispositifs actuels de sauvegarde de données, les bits d'informations sont stockées sous la forme de paroi de domaines dans une couche mince, voire… (more)

▼ Dans les dispositifs actuels de sauvegarde de données, les bits d'informations sont stockées sous la forme de paroi de domaines dans une couche mince, voire des media "patternés". Le support reste donc 2D. De nos jours, la densité de stockage tend vers une valeur maximale qu'il est difficile de dépasser pour des raisons fondamentales et technologiques. Ainsi, récemment des efforts ont été réalisés pour développer des dispositifs 3D qui allient la polyvalence de la mémoire RAM solide avec un coût comparable à celui des disques durs actuels.Un nouveau concept théorique particulièrement intéressant pour une mémoire magnétique en 3D a été proposé en 2004 par S. Parkin et al.. Cette mémoire de type registre à décalage est constituée d'un réseau de nanofils magnétiques verticaux avec une section transversale cylindrique ou bien rectangulaire. Dans ce nouveau type de mémoire, les bits sont codés sous forme d'une série de parois de domaine. Cette dernière peut être déplacée vers une tête de lecture intégrée par des impulsions de courant polarisé en spin de quelques nanosecondes.Les parois de domaines magnétiques dans des nanofils cylindriques ont suscité l'intérêt de la communauté scientifique en raison de leur application possible dans un dispositif fonctionnel ainsi qu'en raison de nouvelles propriétés intéressantes qui résultent du confinement géométrique des parois. A ce jour, seules quelques études expérimentales sur de telles parois de domaines existent. Elles ont mis en évidence la difficulté de maîtriser la propagation de parois dues à des forts effets de piégeage. Jusqu'à présent, l'origine microscopique de ce piégeage n'a été que partiellement comprise. On s'attend à ce qu’indépendamment de la qualité géométrique du fil, la microstructure du matériau puisse jouer un rôle non négligeable.Dans le cadre du projet européen FP7 m3D, l'objectif de mon travail de thèse a été d'étudier la propagation des parois de domaine dans des nanofils cylindriques avec des modulations de diamètre. L'énergie de ces parois de domaine augmentant avec le diamètre du fil, on s'attend à ce que des excroissances (ou des constrictions) agissent comme des barrières d'énergie artificielles (respectivement puits). Par conséquent, une propagation de paroi de domaine contrôlée via la géométrie du fil semble possible.La première partie de mon travail concerne l'optimisation des matériaux. Des fils d'un alliage de NiCo (diamètre de 100-200nm et longueur de plusieurs dizaines de micromètres) avec deux géométries distinctes ont été fabriqués par électrodéposition en collaboration avec le groupe du Prof. J. Bachmann à l' Université d'Erlangen. Pour chaque géométrie, j'ai exploré l'effet de la composition de l'alliage ainsi que d'un recuit sur la microstructure du matériau. Par la suite, la propagation des parois de domaine dans des nanofils individuels a été étudiée sous l'influence d'un champ magnétique quasi-statique ou d'une impulsion de champ magnétique avec une durée d'impulsion de l'ordre de la nanoseconde. Dans la dernière partie de ma thèse,… Advisors/Committee Members: Toussaint, Jean-Christophe (thesis director), Fruchart, Olivier (thesis director).

Subjects/Keywords: Nanofils magnétiques; Dynamique de paroi magnétique; Simulation micromagnétique; Électrodéposition; Magnetic nanowires; Magnetic domain wall dynamics; Micromagnetic modelling; Electrodeposition; 530

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APA · Chicago · MLA · Vancouver · CSE | Export to Zotero / EndNote / Reference Manager

APA (6^th Edition):

Trapp, B. (2018). Nucleation and propagation of magnetic domain walls in cylindrical nanowires with diameter modulations : Nucléation et propagation de parois de domaine magnétiques dans des nanofils cylindriques avec des modulations en diamètre. (Doctoral Dissertation). Université Grenoble Alpes (ComUE). Retrieved from http://www.theses.fr/2018GREAY011

Chicago Manual of Style (16^th Edition):

Trapp, Beatrix. “Nucleation and propagation of magnetic domain walls in cylindrical nanowires with diameter modulations : Nucléation et propagation de parois de domaine magnétiques dans des nanofils cylindriques avec des modulations en diamètre.” 2018. Doctoral Dissertation, Université Grenoble Alpes (ComUE). Accessed March 03, 2021. http://www.theses.fr/2018GREAY011.

MLA Handbook (7^th Edition):

Trapp, Beatrix. “Nucleation and propagation of magnetic domain walls in cylindrical nanowires with diameter modulations : Nucléation et propagation de parois de domaine magnétiques dans des nanofils cylindriques avec des modulations en diamètre.” 2018. Web. 03 Mar 2021.

Vancouver:

Trapp B. Nucleation and propagation of magnetic domain walls in cylindrical nanowires with diameter modulations : Nucléation et propagation de parois de domaine magnétiques dans des nanofils cylindriques avec des modulations en diamètre. [Internet] [Doctoral dissertation]. Université Grenoble Alpes (ComUE); 2018. [cited 2021 Mar 03]. Available from: http://www.theses.fr/2018GREAY011.

Council of Science Editors:

Trapp B. Nucleation and propagation of magnetic domain walls in cylindrical nanowires with diameter modulations : Nucléation et propagation de parois de domaine magnétiques dans des nanofils cylindriques avec des modulations en diamètre. [Doctoral Dissertation]. Université Grenoble Alpes (ComUE); 2018. Available from: http://www.theses.fr/2018GREAY011

KTH

4. Sigurdsson, Ari. Micromagnetic study of spin Hall nano-oscillator arrays and their synchronization dynamics.

Degree: Electrical Engineering and Computer Science (EECS), 2020, KTH

URL: http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-285562

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Spintronics is the study of electron spins and their utilization in electronic devices. Within this field, spin-based oscillators have shown promise for mi- crowave… (more)

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Spintronics is the study of electron spins and their utilization in electronic devices. Within this field, spin-based oscillators have shown promise for mi- crowave signal generation as they can operate at high frequencies, are small in scale and are compatible with modern fabrication techniques. Among these oscillators are the spin Hall nano-oscillators (SHNOs). They are nanoscale thin-film structures driven by pure spin-current injection from a primary con- ductor into a ferromagnetic material. This process can be used to generate microwave signals through oscillations in the material’s magnetization. By constraining the current flow in the device to individual constrictions, an ar- ray arrangement of multiple oscillators can be realized. These oscillators can then be coupled together via their internal interactions to achieve mutual syn- chronization and improve their characteristics.In this work, a versatile micromagnetic modelling procedure for simulating constriction-based SHNOs and their synchronization dynamics in different ar- ray arrangements is presented. A case study of various 2x2 array geometries is conducted along with an exploration of higher-order networks of 4x4, 6x6 and 8x8 oscillators. A perturbative optimization algorithm is developed to improve excitation conditions and drive geometries into a synchronized regime. Lastly, a comparison to nonlinear auto-oscillator theory is presented to illustrate the dependence of generated signals on constriction sizes and the spacing between oscillators. Mutual synchronization between multiple oscillators is achieved and favourable geometry and excitation conditions are defined. The conducted simulations show good agreement with experimental results and illustrate the potential for future studies of SHNO characteristics through micromagnetic modelling.

Spinntronik är ett forskningsområde, som handlar om hur elektronens s.k. spinn kan användas i elektroniska komponenter. Inom detta område har spinnbaserade oscillatorer visat sig ha lovande egenskaper för generering av mikrovågssignaler, eftersom de har höga arbetsfrekvenser, liten storlek och är kompatibla med moderna tillverkningstekniker. En typ av dessa oscillatorer kallas spinn-Hall nano-oscillatorer (SHNO). De är nanometerstora tunnfilms- strukturer, vilka drivs av en ren spinnström, som injiceras från en (metallisk) ledare till en ett ferromagnetiskt material. Denna mekanism kan användas för att skapa mikrovågssignaler genom oscillationer i materialets magnetisering. Genom att begränsa strömflödet i komponenten till enskilda gap kan man skapa en matris med ett stort antal oscillatorer. Dessa oscillatorer kan sedan kopplas till varandra genom interna utbytesmekanismer och på så sätt uppnår man en ömsesidig koppling och förbättrade egenskaper.I detta arbete presenteras ett mångsidigt mikromagnetiskt modelleringsflö- de, för att simulera SHNO:er, baserade på nano-gap, och deras synkronisering i olika matriskonfigurationer. En fallstudie som inkluderar olika 2x2 matris- geometrier har genomförts…

Subjects/Keywords: spintronics; spin Hall nano-oscillators; spin wave; synchronization; micromagnetic modelling.; spinntronik; spinn-Hall nano-oscillatorer; spinn wave; synkronisering; mikromagnetisk modellering.; Computer and Information Sciences; Data- och informationsvetenskap

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APA (6^th Edition):

Sigurdsson, A. (2020). Micromagnetic study of spin Hall nano-oscillator arrays and their synchronization dynamics. (Thesis). KTH. Retrieved from http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-285562

Note: this citation may be lacking information needed for this citation format:
Not specified: Masters Thesis or Doctoral Dissertation

Chicago Manual of Style (16^th Edition):

Sigurdsson, Ari. “Micromagnetic study of spin Hall nano-oscillator arrays and their synchronization dynamics.” 2020. Thesis, KTH. Accessed March 03, 2021. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-285562.

Note: this citation may be lacking information needed for this citation format:
Not specified: Masters Thesis or Doctoral Dissertation

MLA Handbook (7^th Edition):

Sigurdsson, Ari. “Micromagnetic study of spin Hall nano-oscillator arrays and their synchronization dynamics.” 2020. Web. 03 Mar 2021.

Vancouver:

Sigurdsson A. Micromagnetic study of spin Hall nano-oscillator arrays and their synchronization dynamics. [Internet] [Thesis]. KTH; 2020. [cited 2021 Mar 03]. Available from: http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-285562.

Note: this citation may be lacking information needed for this citation format:
Not specified: Masters Thesis or Doctoral Dissertation

Council of Science Editors:

Sigurdsson A. Micromagnetic study of spin Hall nano-oscillator arrays and their synchronization dynamics. [Thesis]. KTH; 2020. Available from: http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-285562

Note: this citation may be lacking information needed for this citation format:
Not specified: Masters Thesis or Doctoral Dissertation

5. Ponomareva, Svetlana. Développement et caractérisation avancée de matériaux magnétiques durs de haute performance : Development and advanced characterization of high performance hard magnetic materials.

Degree: Docteur es, Nanophysique, 2017, Grenoble Alpes; Université polytechnique de Tomsk (Russie)

URL: http://www.theses.fr/2017GREAY035

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L'auteur n'a pas fourni de résumé en français

Nowadays in medicine and biotechnology a wide range of applications involves magnetic micro/nano-object manipulation including remote control… (more)

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L'auteur n'a pas fourni de résumé en français

Nowadays in medicine and biotechnology a wide range of applications involves magnetic micro/nano-object manipulation including remote control of magnetic beads, trapping of drug vectors, magnetic separation of labelled cells and so on. Handling and positioning magnetic particles and elements functionalized with these particles has greatly benefited from advances in microfabrication. Indeed reduction in size of the magnet while maintaining its field strength increases the field gradient. In this context, arrays made of permanent micromagnets are good candidates for magnetic handling devices. They are autonomous, suitable for integration into complex systems and their magnetic action is restricted to the region of interest.In this thesis we have elaborated an original approach based on AFM and MFM for quantitative study of the magnetic force and associated force gradients induced by TMP micromagnet array on an individual magnetic micro/nano-object. For this purpose, we have fabricated smart MFM probes where a single magnetic (sub)micronic sphere was fixed at the tip apex of a non-magnetic probe thanks to a dual beam FIB/SEM machine equipped with a micromanipulator.Scanning Force Microscopy conducted with such probes, the so-called Magnetic Particle Scanning Force Microscopy (MPSFM) was employed for 3D mapping of TMP micromagnets. This procedure involves two main aspects: (i) the quantification of magnetic interaction between micromagnet array and attached microsphere according to the distance between them and (ii) the complementary information about micromagnet array structure. The main advantage of MPSFM is the use of a probe with known magnetization and magnetic volume that in combination with modelling allows interpreting the results ably.We conducted MPSFM on TMP sample with two types of microparticle probes: with superparamagnetic and NdFeB microspheres. The measurements carried out with superparamagnetic microsphere probes reveal attractive forces (up to few tens of nN) while MFM maps obtained with NdFeB microsphere probes reveal attractive and repulsive forces (up to one hundred of nN) for which the nature of interaction is defined by superposition of microsphere and micromagnet array magnetizations. The derived force and its gradient from MFM measurements are in agreement with experiments on microparticle trapping confirming that the strongest magnetic interaction is observed above the TMP sample interfaces, between the areas with opposite magnetization. Thanks to 3D MFM maps, we demonstrated that intensity of magnetic signal decays fast with the distance and depends on micromagnet array and microsphere properties.Besides the magnetic interaction quantification, we obtained new information relevant to TMP sample structure: we observed and quantified the local magnetic roughness and associated fluctuations, in particular in zones of reversed magnetization. The variation of detected signal can reach the same order of magnitude as the signal above the micromagnet…

Advisors/Committee Members: Marchi, Florence (thesis director), Khasanov, Oleg (thesis director).

Subjects/Keywords: Réseau de micro-aimants permanents; Microscopie à force atomique et à force magnétique; Fabrication de la sonde à microparticule; Quantification et cartographie d'interaction à nano-Échelle; Modélisation micromagnétique; Micromagnétisme; Permanent micromagnet array; Atomic and Magnetic Force Microscopy; Microparticle probe fabrication; Nano-Scale interaction quantification and mapping; Micromagnetic modelling; Micromagnetism; 530

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APA (6^th Edition):

Ponomareva, S. (2017). Développement et caractérisation avancée de matériaux magnétiques durs de haute performance : Development and advanced characterization of high performance hard magnetic materials. (Doctoral Dissertation). Grenoble Alpes; Université polytechnique de Tomsk (Russie). Retrieved from http://www.theses.fr/2017GREAY035

Chicago Manual of Style (16^th Edition):

Ponomareva, Svetlana. “Développement et caractérisation avancée de matériaux magnétiques durs de haute performance : Development and advanced characterization of high performance hard magnetic materials.” 2017. Doctoral Dissertation, Grenoble Alpes; Université polytechnique de Tomsk (Russie). Accessed March 03, 2021. http://www.theses.fr/2017GREAY035.

MLA Handbook (7^th Edition):

Ponomareva, Svetlana. “Développement et caractérisation avancée de matériaux magnétiques durs de haute performance : Development and advanced characterization of high performance hard magnetic materials.” 2017. Web. 03 Mar 2021.

Vancouver:

Ponomareva S. Développement et caractérisation avancée de matériaux magnétiques durs de haute performance : Development and advanced characterization of high performance hard magnetic materials. [Internet] [Doctoral dissertation]. Grenoble Alpes; Université polytechnique de Tomsk (Russie); 2017. [cited 2021 Mar 03]. Available from: http://www.theses.fr/2017GREAY035.

Council of Science Editors:

Ponomareva S. Développement et caractérisation avancée de matériaux magnétiques durs de haute performance : Development and advanced characterization of high performance hard magnetic materials. [Doctoral Dissertation]. Grenoble Alpes; Université polytechnique de Tomsk (Russie); 2017. Available from: http://www.theses.fr/2017GREAY035

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