In this book, a team of outstanding scientists in the field of modern magnetic nanotechnologies illustrates the state-of-the-art in several areas of advanced magneto-electronic devices, magnetic micro-electromechanical systems and high density information storage technologies. Providing a unique source of information for the young physicist, chemist or engineer, the book also serves as a crucial reference for the expert scientist and the teacher of advanced university courses.

This book offers a detailed discussion of the complex magnetic behavior of magnetic nanosystems, with its myriad of geometries (e.g. core-shell, heterodimer and dumbbell) and its different applications. It provides a broad overview of the numerous current studies concerned with magnetic nanoparticles, presenting key examples and an in-depth examination of the cutting-edge developments in this field. This contributed volume shares the latest developments in nanomagnetism with a wide audience: from upper undergraduate and graduate students to advanced specialists in both academia and industry. The first three chapters serve as a primer to the more advanced content found later in the book, making it an ideal introductory text for researchers starting in this field. It provides a forum for the critical evaluation of many aspects of complex nanomagnetism that are at the forefront of nanoscience today. It also presents highlights from the extensive literature on the topic, including the latest research in this field.

Divided in two parts, this PhD thesis concerns the magnetization dynamics of magnetic nanoparticles. In the first part, we have described a detailed experimental study of the magnetization dynamics in core/shell CoPt nanoparticles. Towards that goal, we have performed Time Resolved Magneto-Optical Effect measurements using a femtosecond pump and probe set-up with pulse durations and wavelengths : pump 150 fs/400 nm and probe 150 fs/800 nm probe. We studied the different magneto-dynamical processes taking place on short time scales such as : the ultrafast demagnetization and the precession of the magnetization vector. The obtained results indicate a possibility of inducing a supra-crystalline ordering of the nanoparticles due to a mild laser annealing. We showed that there is an important influence of the thermal annealing on the magnetic properties of the nanoparticles. For example, it leads to a magnetic phase transition form super-paramagnetic to ferromagnetic above the room temperature. This ferromagnetism manifested itself as an increase in the magnetic anisotropy of the nanoparticles and in the precession of the magnetization vector induced by the pump pulses. The second part is devoted to the numerical simulations of the magnetization reversal in isolated and interacting nanoparticles. In isolated nanoparticles, the relaxation times follow the Arrhenius law provided by the Néel-Brown's model. To account for the magnetic dipolar interaction, we have introduced a simple and effective model based on the mean field approximation. In general, we have observed deviations from the Arrhenius law, and showed that the dipolar interaction accelerates the reversal process.

In December 2002, the world's first commercial magnetic levitation super-train went into operation in Shanghai. The train is held just above the rails by magnetic levitation (maglev) and can travel at a speed of 400 km/hr, completing the 30km journey from the city to the airport in minutes. Now consumers are enjoying 50 GB hard drives compared to 0.5 GB hard drives ten years ago. Achievements in magnetic materials research have made dreams of a few decades ago reality. The objective of the four volume reference, Handbook of Advanced Magnetic Materials, is to provide a comprehensive review of recent progress in magnetic materials research. Each chapter will have an introduction to give a clear definition of basic and important concepts of the topic. The details of the topic are then elucidated theoretically and experimentally. New ideas for further advancement are then discussed. Sufficient references are also included for those who wish to read the original work. In the last decade, one of the most significant thrust areas of materials research has been nanostructured magnetic materials. There are several critical sizes that control the behavior of a magnetic material, and size effects become especially critical when dimensions approach a few nanometers, where quantum phenomena appear. The first volume of the book, Nanostructured Advanced Magnetic Materials, has therefore been devoted to the recent development of nanostructured magnetic materials, emphasizing size effects. Our understanding of magnetism has advanced with the establishment of the theory of atomic magnetic moments and itinerant magnetism. Simulation is a powerful tool for exploration and explanation of properties of various magnetic materials. Simulation also provides insight for further development of new materials. Naturally, before any simulation can be started, a model must be constructed. This requires that the material be well characterized. Therefore the second volume, Characterization and Simulation provides a comprehensive review of both experimental methods and simulation techniques for the characterization of magnetic materials. After an introduction, each section gives a detailed description of the method and the following sections provide examples and results of the method. Finally further development of the method will be discussed. The success of each type of magnetic material depends on its properties and cost which are directly related to its fabrication process. Processing of a material can be critical for development of artificial materials such as multilayer films, clusters, etc. Moreover, cost-effective processing usually determines whether a material can be commercialized. In recent years processing of materials has continuously evolved from improvement of traditional methods to more sophisticated and novel methods. The objective of the third volume, Processing of Advanced Magnetic Materials, is to provide a comprehensive review of recent developments in processing of advanced magnetic materials. Each chapter will have an introduction and a section to provide a detailed description of the processing method. The following sections give detailed descriptions of the processing, properties and applications of the relevant materials. Finally the potential and limitation of the processing method will be discussed. The properties of a magnetic material can be characterized by intrinsic properties such as anisotropy, saturation magnetization and extrinsic properties such as coercivity. The properties of a magnetic material can be affected by its chemical composition and processing route. With the continuous search for new materials and invention of new processing routes, magnetic properties of materials cover a wide spectrum of soft magnetic materials, hard magnetic materials, recording materials, sensor materials and others. The objective of the fourth volume, Properties and Applications of Advanced Magnetic Materials, is to provide a comprehensive review of recent development of various magnetic materials and their applications. Each chapter will have an introduction of the materials and the principles of their applications. The following sections give a detailed description of the processing, properties and applications. Finally the potential and limitation of the materials will be discussed.

Magnetic materials are vital components of many existing and future applications, from data storage and spin-logic devices, to Terahertz sensors and artificial synapses from neuromorphing computing. Driven by the need to faster responses and high-density storage, the focus of this work is the modeling of thermal and optical excitation of magnetic materials by an external laser source. Many models focus on the use of fields or current as the primary driving force behind the change in magnetization and the models, without taking in account the optical contribution of the light, which has been shown to produce changes in magnetizing on a faster timescale than the ones observed with the use of either current or field. Moreover, granular media are usually modelled using simplistic finite difference approach or numerically intensive finite-elements approach to model every grain. These approach leads to either an unrealistic description of the media (finite-difference) or to an over-sampling of the nodes of the problem, increasing significantly the computational time required to run the simulations. This dissertation improves upon the state of the art of micromagnetic modelling by introducing a Voronoi tessellation model to simulate realistic granular structures at elevated temperature for high anisotropy materials. This approach considers the geometry of the grains for compute the far-field contribution. This approach has been proven effective in modeling realistic media for heat assisted magnetic recording and perpendicular media in general. The model presented it also introduces in the dynamic of the magnetizing the optical contribution and helps to describes complex phenomena like the ultrafast-demagnetization and the helicity dependent optical reversal of magnetic material subjected to an external optical source. While the model provides a qualitative interpretation of the experiments, additional data is required to evaluate the quantitative contribution of the optical excitation and the correctness of the thermal fluctuations. This dissertation is structured as follow. In Chapter 1 and 2 introduce key concepts of magnetism and the basic Micromagnetic model that is going to be used as the basis for the numerical simulations. In Chapter 3 I introduce a micromagnetic code based on Voronoi tessellation and the non-uniform fast Fourier transform (NUFFT) method. The code is capable of efficiently and accurately simulating magnetization dynamics in large and structurally complex granular systems, such as multilayer granular media used for perpendicular magnetic recording, bit patterned media, granular nanowires, and read heads. In these systems the granular microstructure and distributions in grain and interface properties play an important role in device performance. The presented Voronoi simulator allows comprehensive studies to be performed as it accounts for the detailed granular microstructure and distributions that characterize true systems. Simulation time is greatly reduced by a non-uniform fast Fourier transform algorithm and implementation on graphics processing units (GPUs). Simulations of conventional magnetic recording, heat-assisted magnetization reversal, domain wall dynamics in granular nanowires, and particulate tape recording are presented. Chapter 4 explores the generation of electrical field signals in the terahertz frequency (THz) range using antiferromagnets (AFM). Using micromagnetic model simulation, we investigated a potential mechanism for laser-induced THz signals in the AFM phase of FeRh/Pt bilayer films. In the simulations, the FeRh film is modelled as two Fe-sublattices coupled via intra-lattice exchange field and subjected to a sub-picosecond thermal pulse. Our simulation exposes a partial canting between the magnetizations of two Fe-sublattices, within the first picosecond after the excitation. This short-lived state relaxes abruptly into the initial AFM phase, injecting a spin current into the Pt layer via spin pumping, which will eventually be converted into charge current oscillating at THz frequency. Chapters 5 and 6 discuss the phenomenon of all-optical switching of the magnetization in magnetic nanostructures. While all-optical switching of the magnetization in magnetic nanostructures by femtosecond circularly polarized laser pulses without an external magnetic field has been demonstrated in several systems, a theoretical framework that convincingly explain the phenomenon is still missing. In Chapter 5 we propose a theory where the ferromagnetic macrospin ground state is optically excited by the circularly polarized light to a spin reversed state, which is then "Coulomb collapsed" to the magnetization reversed ground state. The optical excitation lasts for the duration of the laser pulse and the system relaxes at a fast rate due to the electron-electron interaction. In Chapter 6 we present a computational model based on this theory. We construct a three-state model for the magnetization dynamics, the Landau-Lifshitz-Lambda (LLL) model, as an ensemble of such states to account for the temperature effects. After the optical excitation lapses, the LLL model reduces to the Landau-Lifshitz-Bloch formulation, allowing to consider the magnetization relaxation dynamics at elevated temperatures. We apply the theory to simulate AOS in FePt films subject to multiple femtosecond circular polarized laser pulses. The simulation results demonstrate characteristic AOS features and agree with recent experiments. Chapter 7 identifies problems in the performance of the established stochastic model in micromagnetics in modeling the thermal fluctuations of longitudinal and transverse components of the magnetization at elevated temperature. A correct estimation of the thermal fluctuation is paramount to develop multiscale atomistic-micromagnetic models. The chapter presents a consistent solution for the diffusion coefficients that satisfy the corresponding Fokker-Planck equation and provide the correct equilibrium magnetization at elevated temperature.

This book presents the structure formation and dynamics of animate and inanimate matter on the nanometre scale. This is a new interdisciplinary field known as Meso-Bio-Nano (MBN) science that lies at the intersection of physics, chemistry, biology and material science. Special attention in the book is devoted to investigations of the structure, properties and dynamics of complex MBN systems by means of photonic, electronic, heavy particle and atomic collisions. This includes problems of fusion and fission, fragmentation, surfaces and interfaces, reactivity, nanoscale phase and morphological transitions, irradiation-driven transformations of complex molecular systems, collective electron excitations, radiation damage and biodamage, channeling phenomena and many more. Emphasis in the book is placed on the theoretical and computational physics research advances in these areas and related state-of-the-art experiments. Particular attention in the book is devoted to the utilization of advanced computational techniques and high-performance computing in studies of the dynamics of systems.