Dynamical depinning of chiral domain walls

The domain wall depinning field represents the minimum magnetic field needed to move a domain wall, typically pinned by samples' disorder or patterned constrictions. Conventionally, such field is considered independent on the Gilbert damping since it is assumed to be the field at which the Zeeman energy equals the pinning energy barrier (both damping independent). Here, we analyse numerically the domain wall depinning field as function of the Gilbert damping in a system with perpendicular magnetic anisotropy and Dzyaloshinskii-Moriya interaction. Contrary to expectations, we find that the depinning field depends on the Gilbert damping and that it strongly decreases for small damping parameters. We explain this dependence with a simple one-dimensional model and we show that the reduction of the depinning field is related to the internal domain wall dynamics, proportional to the Dzyaloshinskii-Moriya interaction, and the finite size of the pinning barriers

Pinned domain wall oscillator as a tuneable direct current spin wave emitter

[EN] Local perturbations in the relative orientation of the magnetic moments in a continuous magnetic system can propagate in the form of waves. These so-called spin waves represent a promising candidate as an information carrier for spin-based low-power applications. A localized, energy-efficient excitation of coherent and short-wavelength spin waves is a crucial technological requirement, and alternatives to excitation via the Oersted field of an alternating current must be explored. Here, we show how a domain wall pinned at a geometrical constriction in a perpendicularly magnetized thin nanowire emits spin waves when forced to rotate by the application of a low direct current flowing along the wire. Spin waves are excited by the in-plane stray field of the rotating domain wall and propagate at an odd harmonic of the domain wall rotation frequency in the direction of the electron's flow. The application of an external field, opposing domain wall depinning induced by the current, breaks the symmetry for spin wave propagation in the two domains, allowing emission in both directions but at different frequencies. The results presented define a new approach to manufacture tuneable high-frequency spin wave emitters of easy fabrication and low power consumption.Comisión Europea (P7-PEOPLE-2013-ITN 608031) Gobierno de España (MAT2014-52477-C5-4-P) Junta de Castilla y Leon (SA282U14, SA090U16

Disorder-induced domain wall velocity shift at high fields in perpendicularly magnetized thin films

[EN]Domain wall dynamics in a perpendicularly magnetized system is studied by means of micromagnetic simulations in which disorder is introduced as a dispersion of both the easy-axis orientation and the anisotropy constant over regions reproducing a granular structure of the material. High field dynamics show a linear velocity-field relationship and an additional grain size dependent velocity shift, weakly dependent on both applied field and intrinsic Gilbert’s damping parameter. We find the origin of this velocity shift in the nonhomogeneous in-plane effective field generated by the tilting of anisotropy easy axis introduced by disorder. We show that a one-dimensional analytical approach cannot predict the observed velocities and we augment it with the additional dissipation of energy arising from internal domain wall dynamics triggered by disorder. This way we prove that the main cause of higher velocity is the ability of the domain wall to irradiate energy into the domains, acquired with a precise feature of disorder.Comisión Europea (P7-PEOPLE-2013-ITN 608031) Gobierno de España (MAT2014-52477-C5-4-P) Junta de Castilla y León (SA282U14 y SA090U16

Reliable Propagation of Magnetic Domain Walls in Cross Structures for Advanced Multiturn Sensors

[EN] We develop and analyze an advanced concept for a domain-wall-based sensing of rotations. Moving domain walls in n closed loops with n - 1 intersecting convolutions by rotating fields, we are able to sense n rotations. By combining loops with coprime numbers of rotations, we create a sensor system allowing for the total counting of millions of turns of a rotating applied magnetic field. We analyze the operation of the sensor and identify the intersecting cross structures as the critical component for reliable operation. Specifically, depending on the orientation of the applied field angle with the magnetization in the branches of the cross, a domain wall is found to propagate in an unwanted direction, yielding failures and counting errors in the device. To overcome this limiting factor, we introduce a specially designed syphon structure to the controlled pinning of the domain wall before the cross and depinning and propagation only for a selected range of applied field angles. By adjusting the syphon and the cross geometry, we find that the optimized combination of both structures prevents failures in the full sensor structure yielding robust operation. Our modeling results show that the optimized element geometry allows for the realization of the sensor with cross-shaped intersections and an operation that is tolerant to inaccuracies of the fabrication.Comisión Europea (P7-PEOPLE-2013-ITN 608031) Gobierno de España (MAT2014-52477-C5-4-P) Junta de Castilla y Leon (SA090U16) European Research Council (MultiRev ERC-2014-PoC 665672) German Research Foundation (SFB TRR173 Spin+X

Geometrical control of pure spin current induced domain wall depinning

[EN] We investigate the pure spin-current assisted depinning of magnetic domain walls in half ring based Py/Al lateral spin valve structures. Our optimized geometry incorporating a patterned notch in the detector electrode, directly below the Al spin conduit, provides a tailored pinning potential for a transverse domain wall and allows for a precise control over the magnetization configuration and as a result the domain wall pinning. Due to the patterned notch, we are able to study the depinning field as a function of the applied external field for certain applied current densities and observe a clear asymmetry for the two opposite field directions. Micromagnetic simulations show that this can be explained by the asymmetry of the pinning potential. By direct comparison of the calculated efficiencies for different external field and spin current directions, we are able to disentangle the different contributions from the spin transfer torque, Joule heating and the Oersted field. The observed high efficiency of the pure spin current induced spin transfer torque allows for a complete depinning of the domain wall at zero external field for a charge current density of 6 1011 A m−2, which is attributed to the optimal control of the position of the domain wall.Comisión Europea (P7-PEOPLE-2013-ITN 608031, FP7-ICT-2009-5) Gobierno de España (MAT2014-52477-C5-4-P) Junta de Castilla y Leon (SA090U16) German Ministry for Education and Science (BMBF) German Research Foundation (DFG) via the DFG collaborative research centre SFB/TRR 173 SPIN+X Graduate School Material Science in Mainz (DFG/GSC 266) European Research Council - MultiRev (665672) Research Center of Innovative and Emerging Materials at Johannes Gutenberg University (CINEMA) German Academic Exchange Service (DAAD) via the SpinNet Program 56268455 French RENATECH networ

Herkunftsnachweis von Südtiroler Äpfeln mittels Analyse des Sr-Isotopenverhältnisses: Grundlagen und praktische Anwendungen

Die meisten Konsumenten interessieren sich immer stärker für die Herkunft ihrer Lebensmittel. Eine vielversprechende Methode, um die Herkunft von landwirtschaftlichen Produkten zu prüfen ist die Analyse des Strontium (87Sr/86Sr)-Isotopenverhältnisses. Das 87Sr/86Sr-Verhältnis einer Pflanze spiegelt jenes des Bodens auf dem sie wächst wider. Der folgende Beitrag zeigt einige Aspekte des 87Sr/86Sr-Verhältnisses, untersucht während eines 3-jährigen Projektes, und seiner Verwendung als geographischen Indikator für Äpfel auf. In einem ersten Experiment betrachteten wir den Einfluss von landwirtschaftlichen Praktiken und des dadurch extern eingebrachten Strontiums, auf das Isotopenverhältnis der Apfelbäume im Gewächshaus. Die Bäume passten sich langsam an das Isotopenverhältnis im Boden an. Die landwirtschaftlichen Anwendungen hatten nur einen geringen Einfluss auf das 87Sr/86Sr-Verhältnis der Pflanze. Im zweiten Experiment wurden Unterschiede im Isotopenverhältnis zwischen Teilproben eines Pflanzenbestandteiles derselben Pflanze ("intra-part"), Unterschiede zwischen den verschiedenen Pflanzenbestandteilen desselben Baumes ("intra-tree"), die Unterschiede zwischen den verschieden Pflanzenbestandteilen unterschiedlicher Bäume derselben Obstanlage ("inter-tree") und ihr Zusammenhang mit dem Isotopenverhältnis im Boden, in jeweils zwei Südtiroler Obstanlagen untersucht. "Intra-part" und "intra-tree" war das 87Sr/86Sr Verhältniss homogen, allerdings konnten wir Unterschiede zwischen den Bäumen ("inter-tree") der beiden Obstanlagen beobachten. Im letzten Experiment wurden die Analysen auf 41 Obstanlagen in Norditalien ausgeweitet. Das 87Sr/86Sr-Verhältnis von Äpfeln mit geographischer Kennzeichnung aus verschiedenen Gebieten, wurde mit jenen ohne Kennzeichnung verglichen. Das Isotopenverhältnis im Apfel korrelierte stark mit jenem des jeweiligen Bodens der entsprechenden Obstanlage. Einige Gebiete hatten ähnliche geologische Eigenschaften und Isotopenverhältnis, wodurch eine eindeutige Unterscheidung nicht für alle Ortschaften möglich war. Trotzdem kann das 87Sr/86Sr-Verhältnis als geographischer Indikator verwendet werden, jedoch sollten in zukünftigen Studien weitere Parameter miteinbezogen werden

Advanced modelling of domain wall dynamics for spintronic devices

[EN]The study of magnetism at the nanoscale has important applications in everyday life. As an example, the vast majority of all data is currently stored in magnetic hard drives, while magnetic sensors are ubiquitous in automotive applications and in the internet of things (IoT) technology. The interaction between the spins of conducting electrons and those of the localized magnetic moments of a ferromagnet is at the base of a new field of studies called Spintronics, whose technological perspectives are to overcome the existing semiconductor technology in terms of power saving, endurance and reliability. Domain wall propagation is the mechanism through which a magnetic system changes its state when its equilibrium is perturbed via an external action and its dynamics is well described using the micromagnetic formalism. Micromagnetic nu- merical simulations are a proficient tool that links experimental observations and theoretical predictions, leading the way in the theoretical understanding of magne- tization dynamics and domain wall motion. In chapter 1 we lay down the fundamental physical concepts of the micromag- netic description of magnetism and present the principal analytical tools used through- out the the rest of the work. Chapter 2 is dedicated to the description of the nu- merical solver used in this work: a custom micromagnetic code based on C++ and CUDA programming languages, developed within the group. Subsequently, we fo- cus on two different problems, making use of the descriptive and predictive power of micromagnetic simulations respectively. In chapter 3, we investigate the effect of disorder on field driven domain wall dynamics in CoFeB thin films. Such structures are the building blocks of MRAM memories and the understanding of field driven domain wall dynamics is a key step towards the optimization of device functionality. Exploiting the ability of mi- cromagnetic simulations to reproduce certain disorder features realistically, we get insight into magnetization dynamics taking place at a scale below instruments reso- lution, uncovering important connections between domain wall dynamics and ma- terial disorder features. Disorder triggers internal domain wall dynamics that gen- erates a faster energy dissipation and a faster domain wall propagation in the high- field regime. In chapter 4, we propose a new spintronic device based on the emission of spin waves by means of the controlled rotation of a domain wall in a ferromagnetic wire. The transmission of information via the periodic oscillatory perturbation of mag- netization, called spin wave, offers new perspectives in the design of low power sensors and emitters. We design a system with realistic material characteristics and investigate how the self oscillatory state of a domain wall, induced by the injection of a charge current, can emit a spin wave signal at frequency of tens of GHz that directly depends on the injected current intensity

Morphogenesis of Isobenefit urbanism: Isobenefit-cities simulator

Isobenefit Urbanism is a spontaneous-guided planning approach based on a morphogenetic code inducing a walking city where one can reach within 1–2km: natural land, shops, amenities, services and places of work. We present the alpha version of a python code for the simulations of Isobenefit urban morphogenesis. It is a code to simulate urban growth scenario by modifying as one wishes the values of the parameters. The latter are related to densities, surface, population size, random factors and built probabilities. This urban growth model results in nearly infinite outputs all satisfying the Isobenefit urbanism objective function

Pinned domain wall oscillator as a tuneable direct current spin wave emitter

Abstract Local perturbations in the relative orientation of the magnetic moments in a continuous magnetic system can propagate in the form of waves. These so-called spin waves represent a promising candidate as an information carrier for spin-based low-power applications. A localized, energy-efficient excitation of coherent and short-wavelength spin waves is a crucial technological requirement, and alternatives to excitation via the Oersted field of an alternating current must be explored. Here, we show how a domain wall pinned at a geometrical constriction in a perpendicularly magnetized thin nanowire emits spin waves when forced to rotate by the application of a low direct current flowing along the wire. Spin waves are excited by the in-plane stray field of the rotating domain wall and propagate at an odd harmonic of the domain wall rotation frequency in the direction of the electron’s flow. The application of an external field, opposing domain wall depinning induced by the current, breaks the symmetry for spin wave propagation in the two domains, allowing emission in both directions but at different frequencies. The results presented define a new approach to manufacture tuneable high-frequency spin wave emitters of easy fabrication and low power consumption