Atomistic Spin Dynamics


Book Description

The purpose of this book is to provide a theoretical foundation and an understanding of atomistic spin-dynamics (ASD), and to give examples of where the atomistic Landau-Lifshitz-Gilbert equation can and should be used. As argued in the text, a description of magnetism in an atomistic way is very natural and allows for an interpretation of experimental results in a clear and deep way. This description also allows for calculations, from first principles, of all parameters needed to perform the spin-dynamics simulations, without using experimental results as input to the simulations. As shown in the book, we are now at a very exciting situation, where it is possible to perform accurate and efficient atomistic simulations on a length- and time-scale which is balancing on the edge of what is experimentally possible. In this way, ASD simulations can both validate and be validated by state-of-the art experiments, and ASD simulations also have the possibility to act as a predictive tool that is able to explain the magnetization dynamics in experimentally inaccessible situations. The purpose of this book has been to communicate technically relevant concepts. An even larger motivation is to communicate an inspiration to magnetism and magnetization dynamics, and the emerging technological fields that one may foresee, e.g. in magnonics, solitonics and skyrmionics.







Spin Dynamics


Book Description

Spin Dynamics: Basics of Nuclear Magnetic Resonance, Second Edition is a comprehensive and modern introduction which focuses on those essential principles and concepts needed for a thorough understanding of the subject, rather than the practical aspects. The quantum theory of nuclear magnets is presented within a strong physical framework, supported by figures. The book assumes only a basic knowledge of complex numbers and matrices, and provides the reader with numerous worked examples and exercises to encourage understanding. With the explicit aim of carefully developing the subject from the beginning, the text starts with coverage of quarks and nucleons and progresses through to a detailed explanation of several important NMR experiments, including NMR imaging, COSY, NOESY and TROSY. Completely revised and updated, the Second Edition features new material on the properties and distributions of isotopes, chemical shift anisotropy and quadrupolar interactions, Pake patterns, spin echoes, slice selection in NMR imaging, and a complete new chapter on the NMR spectroscopy of quadrupolar nuclei. New appendices have been included on Euler angles, and coherence selection by field gradients. As in the first edition, all material is heavily supported by graphics, much of which is new to this edition. Written for undergraduates and postgraduate students taking a first course in NMR spectroscopy and for those needing an up-to-date account of the subject, this multi-disciplinary book will appeal to chemical, physical, material, life, medical, earth and environmental scientists. The detailed physical insights will also make the book of interest for experienced spectroscopists and NMR researchers. • An accessible and carefully written introduction, designed to help students to fully understand this complex and dynamic subject • Takes a multi-disciplinary approach, focusing on basic principles and concepts rather than the more practical aspects • Presents a strong pedagogical approach throughout, with emphasis placed on individual spins to aid understanding • Includes numerous worked examples, problems, further reading and additional notes Praise from the reviews of the First Edition: "This is an excellent book... that many teachers of NMR spectroscopy will cherish... It deserves to be a ‘classic’ among NMR spectroscopy texts." NMR IN BIOMEDICINE "I strongly recommend this book to everyone…it is probably the best modern comprehensive description of the subject." ANGEWANDTE CHEMIE, INTERNATIONAL EDITION




Atomistic Spin Dynamics


Book Description

Several large experimental facilities that focus on detection and probing magnetization dynamics have been realized in Europe, USA and Japan. This book covers theoretical and practical aspects of the vibrant and emerging research field of magnetization dynamics.







Atomistic Spin Dynamics


Book Description







Atomistic Simulation of Collective Excitations in Bcc Iron with Vacancy Defects


Book Description

Utilizing an atomistic computational model which handles both translational and spin degrees of freedom, we have performed combined molecular and spin dynamics simulations to investigate the effect of vacancy defects on spin and lattice excitations in ferromagnetic iron. Interatomic interactions are described using an embedded atom potential and magnetic interactions are governed by a Heisenberg-like Hamiltonian with a coordinate dependent exchange interaction. Fourier transforms of space and time-displaced correlation functions yield the dynamic structure factor, providing characteristic frequencies and lifetimes of the spin wave modes. Comparison of the system containing a 5% randomly distributed vacancy concentration with pure lattice data shows a decrease in frequency as well as a decrease in lifetime for all accessible transverse spin wave excitations. By constructing the spin wave dispersion curve, we observe a decrease in the spin wave stiffness parameter with the introduction of vacancy defects, in agreement with experimental neutron scattering data. Additionally, a rugged spin wave line shape for low-$q$ excitations indicates the presence of multiple localized modes near the defect sites. These induced excitations result in reduced excitation lifetimes due to increased magnon-magnon scattering. We observe further evidence of increased magnon-magnon scattering as additional two-spin-wave annihilation peaks appear in the longitudinal spin wave spectrum under these conditions of impurity. Single vacancy defects, or voids, of varying sizes are introduced into the system, resulting in sharp splitting of long-wavelength excitation line shapes. This splitting behavior is shown to be strongly affected by defect size as well as the size of the surrounding system. Localized correlation function measurements are made in the vicinity of the defect site, showing the existence of a dominant excitation mode in this region. The longitudinal magnetic excitation spectrum contains additional modes which are not present in the pure system due to the increased number of available spin wave annihilation processes. The longitudinal spectrum also reveals splitting of the magnon-phonon coupling mode caused by the defect center.




Reinventing Atomic Magnetic Simulations with Spin-orbit Coupling


Book Description

We propose a powerful extension to the combined molecular and spin dynamics method that fully captures the coupling between the atomic and spin subsystems via spin-orbit interactions. Moreover, the foundation of this method lies in the inclusion of the local magnetic anisotropies that arise as a consequence of the lattice symmetry breaking due to phonons or crystallographic defects. By using canonical simulations of bcc iron with the system coupled to a phonon heat bath, we show that our extension enables the previously unachievable angular momentum exchange between the atomic and spin degrees of freedom.