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Encyclopedia > Spintronics
Unsolved problems in physics: Is it possible to construct a practical electronic device that operates on the spin of the electron, rather than its charge?

Spintronics (a neologism for "spin-based electronics"), also known as magnetoelectronics, is an emergent technology which exploits the quantum spin states of electrons as well as making use of their charge state. The electron spin itself is manifested as a two state magnetic energy system. The discovery of Giant Magnetoresistance in 1988 by Albert Fert et al. is considered as the birth of spintronics. Image File history File links No higher resolution available. ... This is a list of some of the unsolved problems in physics. ... In physics, spin refers to the angular momentum intrinsic to a body, as opposed to orbital angular momentum, which is the motion of its center of mass about an external point. ... e- redirects here. ... In physics, a charge may refer to one of many different quantities, such as the electric charge in electromagnetism or the color charge in quantum chromodynamics. ... A neologism (Greek νεολογισμός [neologismos], from νέος [neos] new + λόγος [logos] word, speech, discourse + suffix -ισμός [-ismos] -ism) is a word, term, or phrase which has been recently created (coined) — often to apply to new concepts, to synthesize pre-existing concepts, or to make older terminology sound more contemporary. ... By the mid 20th century humans had achieved a mastery of technology sufficient to leave the surface of the Earth for the first time and explore space. ... In physics, spin refers to the angular momentum intrinsic to a body, as opposed to orbital angular momentum, which is the motion of its center of mass about an external point. ... e- redirects here. ... In quantum mechanics, a two-state system is a system which has two possible states. ... It has been suggested that this article or section be merged with magnet. ... The Giant Magnetoresistive Effect (GMR) is a quantum mechanical effect observed in thin film structures composed of alternating ferromagnetic and nonmagnetic layers. ... Professor Albert Fert is a French physicist, and one of the discoverers of the Giant magnetoresistive effect which brought about a breakthrough in gigabyte hard disks. ...

Contents

Theory

Spintronics is the ability to change or influence the rotation of an positron.


Electrons have the basic properties of spin, charge, and mass. That the electron has superposition (being everywhere) at the sameforget it, where theory states you can only know certain values but not simultaneously, one pair is momentum and position, and the other is energy and time. Electrons have 2 spin states +spin up and -spin down which are usually found in paired electrons. No two electrons can occupy the same quantum state. Spin up and spin down states of fermions have different energies depending on whether or not the spin states are aligned with the magnetic field or not. Electrons absorb photons quantum energy to change valence orbits, and they lose spin coherence by colliding with mutually resonant photons frequencies causing the electron to spin flip by energy transfer through mutual spin-orbit coupling and photon emission.


In order to make a spintronic device, the primary requirement is to have a system that can generate a current of spin polarized electrons, and a system that is sensitive to the spin polarization of the electrons. Most devices also have a unit in between that changes the current of electrons depending on the spin states.


The simplest method of generating a spin polarised current is to inject the current through a ferromagnetic material. The most common application of this effect is a giant magnetoresistance (GMR) device. A typical GMR device consists of at least two layers of ferromagnetic materials separated by a conductive spacer layer, e.g., a copper spacer layer. When the two magnetization vectors of the ferromagnetic layers are aligned, then an electrical current will flow freely, whereas if the magnetization vectors are antiparallel then the resistance of the system is higher. Ferromagnetism is a phenomenon by which a material can exhibit a spontaneous magnetization, and is one of the strongest forms of magnetism. ... Founding results of Fert The Giant Magnetoresistance (GMR) is a quantum mechanical effect observed in thin film structures composed of alternating ferromagnetic and nonmagnetic metal layers. ... In electricity, current refers to electric current, which is the flow of electric charge. ...


Two variants of GMR have been applied in devices, current-in-plane where the electric current flows parallel to the layers and current-perpendicular-to-the-plane where the electric current flows in a direction perpendicular to the layers.


Applications

Spintronic devices are used in the field of mass-storage devices; recently (in 2002) IBM scientists announced that they could compress massive amounts of data into a small area, at approximately one trillion bits per square inch (1.5 Gbit/mm²) or roughly 1 TB on a single sided 3.5" diameter disc. The storage density of hard drives is rapidly increasing along an exponential growth curve. The doubling period for the areal density of information storage is twelve months, much shorter than Moore's Law, which observes that the number of transistors in an integrated circuit doubles every eighteen months. Also the hard disk drives use a spin effect to function, the Giant magnetoresistive effect (see below). A mass-storage device is usually a very high capacity computer storage medium that is an order of magnitude less costly than a hard disk or other primary storage media. ... Also see: 2002 (number). ... International Business Machines Corporation (IBM, or colloquially, Big Blue) (NYSE: IBM) (incorporated June 15, 1911, in operation since 1888) is headquartered in Armonk, New York, USA. The company manufactures and sells computer hardware, software, and services. ... Typical hard drives of the mid-1990s. ... Gordon Moores original graph from 1965 Growth of transistor counts for Intel processors (dots) and Moores Law (upper line=18 months; lower line=24 months) For the observation regarding information retrieval, see Mooers Law. ... Integrated circuit of Atmel Diopsis 740 System on Chip showing memory blocks, logic and input/output pads around the periphery Microchips with a transparent window, showing the integrated circuit inside. ... Founding results of Fert The Giant Magnetoresistance (GMR) is a quantum mechanical effect observed in thin film structures composed of alternating ferromagnetic and nonmagnetic metal layers. ...


The most successful spintronic device to date is the spin valve, a GMR device. This device utilizes a layered structure of thin films of magnetic materials, which changes electrical resistance depending on applied magnetic field direction. In a spin valve, one of the ferromagnetic layers is "pinned" so its magnetization direction remains fixed and the other ferromagnetic layer is "free" to rotate with the application of a magnetic field. A spin valve is a device consisting of two or more conducting magnetic materials, that alternates its electrical resistance (from low to high or high to low) depending on the alignment of the magnetic layers. ...


When the magnetic field aligns the free layer and the pinned layer magnetization vectors, the electrical resistance of the device is at its minimum. When the magnetic field causes the free layer magnetization vector to rotate in a direction antiparallel to the pinned layer magnetization vector, the electrical resistance of the device increases due to spin dependent scattering. The magnitude of the change, (Antiparallel Resistance - Parallel Resistance) / Parallel Resistance x 100% is called the GMR ratio. Electrical resistance is a measure of the degree to which an electrical component opposes the passage of current. ...


Devices have been demonstrated with GMR ratios as high as 200% with typical values greater than 10%. This is a vast improvement over the anisotropic magnetoresistance effect in single layer materials which is usually less than 3%. Spin valves can be designed with magnetically soft free layers which have a sensitive response to very weak fields (such as those originating from tiny magnetic bits on a computer disk), and have replaced anisotropic magnetoresistance sensors in computer hard disk drive heads since the late 1990s. Microphotograph of a hard disk head. ...


Future applications may include a spin-based transistor which requires the development of magnetic semiconductors exhibiting room temperature ferromagnetism. The operation of MRAM or magnetic random access memory is also based on spintronic principles. Assorted discrete transistors A transistor is a semiconductor device, commonly used as an amplifier or an electrically controlled switch. ... Magnetic semiconductors are materials that exhibit both ferromagnetism (or a similar response) and useful semiconductor properties. ... Ferromagnetism is the phenomenon by which materials, such as iron, in an external magnetic field become magnetized and remain magnetized for a period after the material is no longer in the field. ... Magnetoresistive Random Access Memory (MRAM) is a non-volatile computer memory (NVRAM) technology, which has been in development since the 1990s. ...


Multiferroics which have properties of being able to change internal molecular geometry under electrostatic or electromagnetic influence is a hotbed of research at several universities.See [1] for more details; the physics of spintronics with animation.


See also

‹The template below has been proposed for deletion. ... The introduction to this article provides insufficient context for those unfamiliar with the subject matter. ... A BOINC distributed computing project Spinhenge@home is a distributed computing project for the BOINC client. ...

Further reading

  • Ultrafast Manipulation of Electron Spin Coherence. J. A. Gupta, R. Knobel, N. Samarth and D. D. Awschalom in Science, Vol. 292, pages 2458-2461; June 29, 2001.
  • Spintronics: A Spin-Based Electronics Vision for the Future. S. A. Wolf et al, Science 294, 1488-1495 (2001)
  • How to Create a Spin Current. P. Sharma, Science 307, 531-533 (2005)
  • Search Google Scholar for highly cited articles with query: spintronics OR magnetoelectronics OR "spin based electronics"

External links

  • Scientific American (2002)
  • IBM (2003)
  • Wired: update on MRAMs, 2003 Jul
  • Spintronics research targets GaAs.
  • Spintronics at SUNY Albany's College of Nanoscale Science and Engineering
  • Spintronics information community site
  • Optical Spintronics Data Storage

 
 

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