Concepts In Spin Electronics
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Concepts in Spin Electronics
Nowadays information technology is based on semiconductor and ferromagnetic materials. Information processing and computation are based on electron charge in semiconductor transistors and integrated circuits, and information is stored on magnetic high-density hard disks based on the physics of the electron spins. Recently, a new branch of physics and nanotechnology, called magneto-electronics, spintronics, or spin electronics, has emerged, which aims at simultaneously exploiting both the charge and the spin of electrons in the same device. A broader goal is to develop new functionality that does not exist separately in a ferromagnet or a semiconductor. The aim of this book is to present new directions in the development of spin electronics in both the basic physics and the technology which will become the foundation of future electronics.
Nanomagnetism and Spintronics
Author: André Thiaville
language: en
Publisher: Elsevier Inc. Chapters
Release Date: 2013-10-07
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.
Nanomagnetism and Spintronics
Author: Hiroshi Kohno
language: en
Publisher: Elsevier Inc. Chapters
Release Date: 2013-10-07
Current-driven domain-wall motion and related phenomena are reviewed from a theoretical point of view. In the first part, the dynamics of a rigid domain wall is described based on the collective-coordinate method. After an elementary introduction, the equations of motion are derived for a wall under current, whose effects enter as a spin-transfer effect and a momentum-transfer effect (force). The wall motion is studied in detail, and several depinning mechanisms are found. In the second part, a microscopic derivation of spin torques is described for slowly varying magnetic texture. In addition to the well-established spin-transfer torque, two new torques are shown to arise from the spin-relaxation process and the nonadiabatic process (reflection) of conduction electrons. These new torques act as forces on a rigid wall. Some related topics are described in the third part, which includes current-driven dynamics of magnetic vortices and the current-induced spin-wave instability and domain-wall nucleation.