CORAL GABLES, FL. (March 11, 2009)—Researchers at the University of Miami and at the Universities of Tokyo and Tohoku, Japan, have been able to prove the existence of a "spin battery," a battery that is "charged" by applying a large magnetic field to nano-magnets in a device called a magnetic tunnel junction (MTJ). The new technology is a step towards the creation of computer hard drives with no moving parts, which would be much faster, less expensive and use less energy than current ones. In the future, the new battery could be developed to power cars. The study will be published in an upcoming issue of Nature and is available in an online advance publication of the journal.
The device created by University of Miami Physicist Stewart E. Barnes, of the College of Arts and Sciences and his collaborators can store energy in magnets rather than through chemical reactions. Like a winding up toy car, the spin battery is "wound up" by applying a large magnetic field --no chemistry involved. The device is potentially better than anything found so far, said Barnes.
"We had anticipated the effect, but the device produced a voltage over a hundred times too big and for tens of minutes, rather than for milliseconds as we had expected," Barnes said. "That this was counterintuitive is what lead to our theoretical understanding of what was really going on."
The secret behind this technology is the use of nano-magnets to induce an electromotive force. It uses the same principles as those in a conventional battery, except in a more direct fashion. The energy stored in a battery, be it in an iPod or an electric car, is in the form of chemical energy. When something is turned "on" there is a chemical reaction which occurs and produces an electric current. The new technology converts the magnetic energy directly into electrical energy, without a chemical reaction. The electrical current made in this process is called a spin polarized current and finds use in a new technology called "spintronics."
The new discovery advances our understanding of the way magnets work and its immediate application is to use the MTJs as electronic elements which work in different ways to conventional transistors. Although the actual device has a diameter about that of a human hair and cannot even light up an LED (light-emitting diode--a light source used as electronic component), the energy that might be stored in this way could potentially run a car for miles. The possibilities are endless, Barnes said.
"There are magnets hidden away in many things, for example there are several in a mobile telephone, many in a car, and they are what keeps your refrigerator closed," he said. "There are so many that even a small change in the way we understand of how they work, and which might lead to only a very small improvement in future machines, has a significant financial and energetic impact."
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http://www.eurekalert.org/pub_releases/2009-03/uom-uom_1031109.phpGaMnAs
Although there are a number of different magnetic semiconductors, in the short time since its invention (Ga,Mn)As has become the most popular and widely studied for a number of reasons. Firstly, it is based on the world's second favourite semiconductor, GaAs, and as such is readily compatible with existing semiconductor technologies. Secondly, many dilute magnetic semiconductors (DMSs), such as the majority of those based on II-VI semiconductors, are only paramagnetic.<1> (Ga,Mn)As, on the other hand, is ferromagnetic, and hence exhibits hysteretic magnetisation behaviour. This memory effect is of importance for the creation of persistent devices. A third key feature of (Ga,Mn)As is that not only do the manganese atoms provide a magnetic moment, each also acts as an acceptor, making it a p-type material. The presence of carriers allows the material to be used for spin-polarised currents. In contrast, many other ferromagnetic DMSs are strongly insulating<2><3> and so do not possess free carriers. When all these factors are taken together, (Ga,Mn)As appears to be an exceptionally good candidate as a spintronic material.
http://en.wikipedia.org/wiki/Gallium_manganese_arsenideFabrication and Characterization of MnAs/GaAs Heterostructures
for Studies of One-Dimensional Spin Transport
David Toyli
Physics, University of Minnesota
MnAs is an attractive material for use in studies of ferromagnet/semiconductor heterostructures. Its room- temperature ferromagnetic properties and its ease of growth by molecular beam epitaxy (MBE) on arsenide semiconductors have motivated its use as a source of spin-polarized electrons in experiments in the field of spintronics <1>. In this work we present results on the fabrication and characterization of MnAs/GaAs nanowires. Freestanding nanowires with diameters down to 75 nm were fabricated and magnetic force microscopy (MFM) studies of nanowires with diameters down to 100 nm were conducted. Future experiments utilizing these nanostructures will provide information on the influence of geometrical confinement on the transport of spin- polarized electrons. Recent experiments on electron spin dynamics in InGaAs lateral channels have demonstrated one-dimensional electron spin dynamics in channels an order of magnitude greater than the electron mean free path <2>. The structures fabricated in this work could be used to do electrical spin transport experiments to further understand the effects of reduced dimensionality on spin- polarized transport in semiconductors.
http://www.nnin.org/doc/NNINreu06Toyli.pdfScienceDaily (Feb. 15, 2008) — Graphene is a nanomaterial combining very simple atomic structure with intriguingly complex and largely unexplored physics. Since its first isolation about four years ago researchers suggested a large number of applications for this material in anticipation of future technological revolutions. In particular, graphene is considered as a potential candidate for replacing silicon in future electronic devices.
http://www.sciencedaily.com/releases/2008/02/080210124107.htmhttp://emsnews.wordpress.com/2009/03/16/battery-systems-using-exotic-energy-sources/#more-2348