In all current data storage devices, the information bits are stored in form of domain walls in a thin film or in patterned media on a two-dimensional surface . Within the next decade, further increase of the storage density in these devices is expected to come to a halt due to several fundamental and technological issues. Thus there have recently been efforts to develop three-dimensional devices combining the versatility of solid state RAM with the cost efficiency of common hard disk drives.A particularly interesting theoretical concept for a three-dimensional magnetic memory has been proposed in 2004 by S. Parkin et al. . Their racetrack memory consists of a vertical array of magnetic nanowires with either cylindrical or rectangular cross section. The bits are encoded in a series of up to 100 domain walls per wire. Using nanosecond spin polarized current pulses these walls are shifted past an integrated read head.Magnetic domain walls in cylindrical nanowires have raised the interest of the scientific community due to their possible application in a functional device as well as due to exciting new properties which arise from the geometric confinement. Up to date, only a few pioneering experimental studies on such domain walls exist. They indicate strong pinning effects preventing a deterministic domain wall propagation. So far the microscopic origin of this pinning has only partially been understood. It is expected however that beside the wire geometry the material microstructure may play a considerable role.Situated within the framework of the European FP 7 project m3D, the objective of my work has been to investigate the domain wall propagation in cylindrical nanowires with diameter modulations by means of magnetic force microscopy and micromagnetic simulation. As the domain wall energy increases with the wire diameter, protrusions (resp. notches) are expected to act as an artificial energy barrier (resp. well). Consequently, a deterministic domain wall propagation controlled via the wire geometry seems possible.A first part of my work concerns material optimization. For this, NiCo alloy wires (100-200nm diameter and multiple tens of micrometers in length) with two distinct geometries have been fabricated by template assisted electrodeposition (Chemist collaborators at Univ. Erlangen, Prof. J.Bachmann). I have then explored the impact of the alloy composition as well as of possible post-fabrication annealing on the material microstructure. Subsequently, domain wall propagation in individual nanowires has been investigated under the influence of either a quasistatic magnetic field or a nanosecond magnetic field pulse. In addition I have performed complementary micromagnetic simulations to study the effect of the modulation geometry on the domain wall pinning.

PhD dissertation awarded with the International Mention in the PhD Programme Condensed Matter Physics, Nanoscience and Biophysics of the Autonomous University of Madrid in year 2019. Explore this PhD dissertation, awarded with an International Mention in the PhD Programm Condensed Matter Physics, Nanoscience, and Biophysics from the Autonomous University of Madrid in 2019. This edition has enhanced readability with refreshing redesign and unique botanic motifs from the international expedition led by Jose Mutis that aim to inspire scientists and science lovers. This thesis delves into micromagnetic and analytical modelling of magnetization processes in three-dimensional nanomagnetism, focusing on design for nanotechnological applications of cylindrical nanowires. The exploration covers topics like remanent states, hysteresis processes, and pinning properties of nanowires of magnetic alloys and several geometries. Results provide a foundation for applications such as 3D magnetic memories, sensors, permanent magnets, bio-magnetic innovations, and water purification. Overall, this book communicates excellence in Research with an appealing design that covey an innovative approach of research for all readers.

Magnetic Nano-and Microwires: Design, Synthesis, Properties and Applications, Second Edition, reviews the growth and processing of nanowires and nanowire heterostructures using such methods as sol-gel and electrodeposition, focused-electron/ion-beam-induced deposition, epitaxial growth by chemical vapor transport, and more. Other sections cover engineering nanoporous anodic alumina, discuss magnetic and transport properties, domains, domain walls in nano-and microwires. and provide updates on skyrmions, domain walls, magnetism and transport, and the latest techniques to characterize and analyze these effects. Final sections cover applications, both current and emerging, and new chapters on memory, sensor, thermoelectric and nanorobotics applications. This book will be an ideal resource for academics and industry professionals working in the disciplines of materials science, physics, chemistry, electrical and electronic engineering and nanoscience. Details the multiple key techniques for the growth, processing and characterization of nanowires and microwires Reviews the principles and difficulties involved in applying magnetic nano- and microwires to a wide range of applications, also including biomedical and sensing applications Discusses magnetism and transport in nanowires, skyrmions and domain walls in nanowires and the latest innovations in magnetic imaging

For both fundamental research and technological applications it is of interest to understand and control the magnetization reversal and the pinning of domain walls in ferromagnetic nanostructures. The present work provides new insights into the magnetic behavior of electrochemically synthesized nanowires by applying established methods such as magnetoresistance measurements and magnetic force microscopy as well as a novel photoemission electron microscopy method developed at the synchrotron light source BESSY II in Berlin, Germany. A main focus lies on the feasability of domain wall preparation in cylindrical nanowires with one or more diameter modulations. Furthermore, domain nucleation and pinning of domain walls in flat Co/Pt multilayer wires with perpendicular magnetic anisotropy is studied by transmission x-ray microscopy.

Magnetic Nano-and Microwires: Design, Synthesis, Properties and Applications, Second Edition, reviews the growth and processing of nanowires and nanowire heterostructures using such methods as sol-gel and electrodeposition, focused-electron/ion-beam-induced deposition, epitaxial growth by chemical vapor transport, and more. Other sections cover engineering nanoporous anodic alumina, discuss magnetic and transport properties, domains, domain walls in nano-and microwires. and provide updates on skyrmions, domain walls, magnetism and transport, and the latest techniques to characterize and analyze these effects. Final sections cover applications, both current and emerging, and new chapters on memory, sensor, thermoelectric and nanorobotics applications. This book will be an ideal resource for academics and industry professionals working in the disciplines of materials science, physics, chemistry, electrical and electronic engineering and nanoscience. Details the multiple key techniques for the growth, processing and characterization of nanowires and microwires Reviews the principles and difficulties involved in applying magnetic nano- and microwires to a wide range of applications, also including biomedical and sensing applications Discusses magnetism and transport in nanowires, skyrmions and domain walls in nanowires and the latest innovations in magnetic imaging

Cylindrical magnetic nanowires are a prototypical system for exploring the physics of three-dimensional magnetization dynamics, and are also proposed as building blocks for three-dimensional storage devices. Among other curvature-induced effects, they can host a unique type of magnetic domain wall (DW) known as Bloch-Point-Wall (BPW), whose topology allows for ultra-fast DW motion, thanks to the significant delay in the Walker instability threshold. A crucial feature of BPWs and other spin textures in nanowires, common to three-dimensional systems, is the curling of magnetization induced by dipolar energy. Another key featureis the long-overlooked strong OErsted field that arises when an electric current flows in the wire, which plays a key role by directly coupling to curling structures. Recent pioneering work in the host group has shown experimental BPW motion under spin-transfer-torque with velocities of several hundred of m/s, but with stochastic pinning. Simulations suggest a non-trivial underlying mechanism for the switching of circulation in the case of an initially-antiparallel OErsted field...

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