Nanomagnetism And Spintronics

Spintronics is a newly developing area in the field of magnetism, in which the interplay of magnetism and transport phenomena is studied experimentally and theoretically. This book introduces the recent progresses in the research relating to spintronics. * Presents in-depth analysis of this fascinating and technologically important new branch of nanoscience * Edited text with contributions from acknowledged leaders in the field * This handbook and guide will appeal to students and researchers in the fields of electronic devices and materials

The concise and accessible chapters of Nanomagnetism and Spintronics, Second Edition, cover the most recent research in areas of spin-current generation, spin-calorimetric effect, voltage effects on magnetic properties, spin-injection phenomena, giant magnetoresistance (GMR), and tunnel magnetoresistance (TMR). Spintronics is a cutting-edge area in the field of magnetism that studies the interplay of magnetism and transport phenomena, demonstrating how electrons not only have charge but also spin. This second edition provides the background to understand this novel physical phenomenon and focuses on the most recent developments and research relating to spintronics. This exciting new edition is an essential resource for graduate students, researchers, and professionals in industry who want to understand the concepts of spintronics, and keep up with recent research, all in one volume. Provides a concise, thorough evaluation of current research Surveys the important findings up to 2012 Examines the future of devices and the importance of spin current

Dynamical behavior of magnetic domain wall (DW) is one of the main issues in the field of spintronics. In this chapter, several experimental studies in DW dynamics in nanomagnetic systems are described. For the study of DW motion in nanoscale wires, samples with a trilayer structure, ferromagnetic/nonmagnetic/ferromagnetic, were prepared and the position of DW was estimated from electrical resistance measurements using giant magnetoresistance principle. The velocity of DW driven by an external field has been evaluated from the resistance change. On the other hand, current-driven DW motion in a single wire of ferromagnetic layer was studied by magnetic force microscopy (MFM). All-electrical control and local detection of multiple magnetic DWs are also shown. Magnetic vortex structures are realized in nanoscale ferromagnetic dot systems. The behavior of vortex core magnetization was observed by MFM. Recent topics such as the switching of vortex core driven by a high frequency AC are introduced. Furthermore, all-electrical operation of a magnetic vortex core memory cell is demonstrated.

Novel magnetotransport phenomena appear when magnet sizes become nanoscale. Typical examples of such phenomena are giant magnetoresistance (GMR) in magnetic multilayers, tunnel magnetoresistance (TMR) in ferromagnetic tunnel junctions, and ballistic magnetoresistance (BMR) in magnetic nanocontacts. In this chapter, we first briefly review the relationship between spin-dependent resistivity and electronic structures in metals and alloys, and describe microscopic methods for investigating electrical transport. We then review the essential aspects of GMR, TMR, and BMR, emphasizing the role of the electronic structures of the constituent metals of these junctions and the effects of roughness on the electrical resistivity (or resistance). The important factors that control GMR are shown to be the spin-dependent random potential at interfaces and band matching/mismatching between magnetic and nonmagnetic layers. For TMR, several factors are shown to be important in determining the MR ratio, including the shape of the Fermi surface of the electrodes, the symmetry of the wave functions, electron scattering at interfaces, and spin-slip tunneling. An interpretation of TMR in Fe/MgO/Fe and of an oscillation of TMR is presented. TMR in granular films and in the Coulomb-blockade regime is also described. We also provide a brief explanation for other MR effects, such as normal MR, anisotropic MR (AMR) and colossal MR (CMR) in order to clarify the essential difference between these MRs and GMR, TMR, and BMR. These MR effects are attributed to the spin-dependent electrical currents produced in metallic ferromagnets. After the discovery of these different MR effects, the role of spin current was proposed, for example, spin Hall effect and the effects of spin transfer torque, which will be briefly explained in this chapter. The former orginates from the spin–orbit interaction, and can be observed even in nonmagnetic metals and semiconductors. It is closely related to the anomalous Hall effect observed in ferromagnetic metals. The spin transfer torque is an inverse effect of the MR. The MR is the resistivity change produced by magnetization rotation in ferromagnetic junctions, while the spin transfer torque is an effect in which spin-polarized current makes the magnetization rotate. Finally, we briefly introduce the coupled effects of spin, charge, and heat transport, which are called spin caloritronics.

Nanomagnetism and spintronics are two close subfields of nanoscience, explaining the effect of substantial magnetic properties of matter when the materials fabrication is realized at a comparable length size. Nanomagnetism deals with the magnetic phenomena specific to the structures having dimensions in the submicron range. The fact that the electronic transport properties of materials are dependent on the magnetic properties' artificial nanostructures, i.e., giant magnetoresistance (GMR) or tunneling magnetoresistance (TMR), has revolutionized spintronics science and technology. This book explains the concepts of nanomagnetism and spintronics by viewing the most recent research works from internationally distinguished research groups. Placing special emphasis on crucial fundamental and technical aspects of nanomagnetism and spintronics, it serves as a one-stop reference for universities offering postgraduate programs in nanotechnology or related disciplines. This unique book deals with all three stages required for conducting research in nanomagnetism and spintronics including fabrication, characterization and applications of nanomagnetic and spintronics materials, providing general concepts and an insightful overview of this subject for research students and scientists from different backgrounds investigating the multidisciplinary area of nanotechnology.

This overview is a brief introduction to the subjects covered by this book, nanomagnetism and spintronics. The discovery of giant magnetoresistance (GMR) effect is described together with a short summary of the studies prior to the experiments on GMR. Studies on various kinds of magnetoresistance (MR) effect that were inspired by the GMR effect are reviewed and recent topics are introduced. In many novel phenomena involving the interplay of electric conductance and magnetization, the role of the “spin current” has been revealed to be important and the possibility for exploiting these phenomena in spintronics devices has been suggested. Nanoscale devices are indispensable to fundamental studies on spintronics and also to various technical devices, and therefore gaining an understanding of nanomagnetism is a crucial current issue. At the end of this section, the scope of this book is described in brief with the content of each chapter.

This first book to focus on the applications of nanomagnetism presents those already realized while also suggesting bold ideas for further breakthroughs. The first part is devoted to the concept of spin electronics and its use for data storage and magnetic sensing, while the second part concentrates on magnetic nanoparticles and their use in industrial environment, biological and medical applications. The third, more prospective part goes on to describe emerging applications related to spin current creation and manipulation, dynamics, spin waves and binary logic based on nano-scale magnetism. With its unique choice of topics and authors, this will appeal to academic as well as corporate researchers in a wide range of disciplines from physics via materials science to engineering, chemistry and life science.

Spin-transfer torque manifests itself in two main geometries, either submicrometer diameter pillars composed of magnetic multilayers, flooded by a current perpendicular to plane (CPP), or nanowires with current flowing in their plane (CIP). The first situation can be described rather well, from the magnetic point of view, in the framework of the macrospin model (see by Y. Suzuki). In the latter case, the typical situation is that of a magnetic domain wall under CIP current, with many internal degrees of freedom. In by H. Kohno and G. Tatara, a simplest model of the domain wall, called collective coordinates model, has been introduced to study this question. In this chapter, we will address the entire manifold of the degrees of freedom in the domain wall by micromagnetic numerical simulations, and apply this to the physics of CIP spin transfer in magnetic domain walls. We will consider soft magnetic materials only, where domain wall structures and dynamics are controlled by magnetostatics. This corresponds to the largest part of experiments that have been performed up to now, soft magnetic materials having generally lower coercive forces and domain wall propagation fields. The experimental counterpart to this chapter can be found in , by T. Ono and T. Shinjo. After briefly introducing micromagnetics and the typology of domain walls in samples shaped into nanostrips, we start by reviewing the field-driven dynamics in such samples. This situation was indeed considered first, historically, and led to the introduction of several useful concepts. Prominent among them are the separation between steady-state and precessional regimes, and the existence of a maximum velocity for a domain wall. The spin-transfer torque-induced domain wall dynamics will then be addressed, considering first the implementation of the CIP spin transfer torque in micromagnetics, with several components as introduced by theory. Comparison will be made to the field-driven case, with similarities and differences highlighted. In the nascent field of nanomagnetism and spintronics, micromagnetics can be considered to play the role of a translator. There are on one side experiments and on the other side theories about interaction between magnetization and spin-polarized electrical currents. Micromagnetics is a tool that translates the equations of the latter into quantitative predictions that can be compared to the former. Considering the present state of the subject of this book, with rapidly advancing experiments and theories, keeping in touch those two aspects of research is very important for its sound development. This is the objective of this chapter.