Spintronics

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Spintronics - Wikipedia, the free encyclopedia
Spintronics at SUNY Albany's College of Nanoscale Science and Engineering ... IBM to use 'spintronics' to increase computer memory capacity (April 12, 2008) ...
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Spintronics | Scientific American
Scientific American has thousands of articles like "Spintronics". Unique insights about developments in science and technology for more than 150 years.
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Spintronics-Info | Your source for Spintronics information, news ...
Spintronics-info, with information, news and more resources ... World's First 300-mm Ready Ion Beam Deposition System for Spintronics Development ...
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Spintronics
Spintronics paves the way to quantum computation. Conclusion. Authors ' ... The field of spintronics is extremely young and it is difficult to predict how it ...
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IBM Journal of Research and Development | Vol. 50, No. 1, 2006 ...
IBM Journal of Research and Development issue 50-1 Table of Contents ... IBM Research: Magnetoelectronics and Spintronics. IBM Research: MRAM ...
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Introduction to Spintronics
Spintronics, or spin electronics, refers to the study of the role played by ... Currently the spintronics research effort in our group focuses on the following ...
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Spintronics
Spintronics has been recognized as one of the demanding area of researches which ... Spintronics is a multi disciplinary area of research and requires a coordinated ...
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Simplified Spintronics
One of these areas is that of spintronics. ... A simpler definition is that spintronics is a "new branch of electronics in ... So how does spintronics work? ...
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Spintronics
in 1996, spintronics (the word coined by S. Wolf) ... spintronics. Major advances in electron spin trans ... Spintronics: A spin-based electronics vision for the ...
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Spintronics (a neologism for "spin-based electronics"), also known as magnetoelectronics, is an emerging technology which exploits the quantum spin (physics) states of electrons as well as making use of their charge state. The electron spin itself is manifested as a two state system magnetism energy system.

The discovery of giant magnetoresistance in 1988 by Albert Fert et al. and Peter Grünberg et al. independently is considered as the birth of spintronics.

Theory Spintronics describes technology with the ability to change or influence the quantum spin state of electrons.

Electrons exhibit the basic properties of spin, charge, and mass. When the intrinsic spin of an electron is measured, it is found in one of two spin states, which we denote as spin up and spin down. Since the Pauli Exclusion Principle dictates that the quantum-mechanical wavefunction of two paired fermions must be antisymmetric, no two electrons can occupy the same quantum state, implying that an entangled pair of electrons cannot have the same spin. There is generally a splitting of the spin-up and spin-down energy levels via the Zeeman effect, so electrons with their spins aligned with an external field are less energetic than electrons with their spins anti-aligned. Electrons absorb or emit photon (quanta of electromagnetic energy) to change valence orbits, and they lose spin coherence by interacting with mutually resonant photon frequencies, causing the electrons to spin flip by energy transfer, through mutual spin-orbit coupling, and through 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. Dmitry Grinevich was one of the original scientists who helped discover the Theory of Polarized Electrons; this theory helped create some of the first spintronics devices ever created (see further reading for details). 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 magnetoresistive effect (GMR) device. A typical GMR device consists of at least two layers of ferromagnetic materials separated by a spacer layer. When the two magnetization vectors of the ferromagnetic layers are aligned, then an electrical current (electricity) will flow freely, whereas if the magnetization vectors are antiparallel then the resistance of the system is higher.

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) International Business Machines 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).

The most successful spintronic device to date is the spin valve. 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.

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.

Devices have been demonstrated with GMR ratios as high as 200% with typical values greater than 10%. This is a vast improvement over the Anisotropy 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 disk read-and-write head since the late 1990s.

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.

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 for more details; the physics of spintronics with animation.

See also

Spin pumping
Spin transfer
Spinhenge@Home