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Power Science

"Spin Battery" Effect Discovered 234

Posted by kdawson
from the usual-caveats-apply dept.
An anonymous reader writes "Researchers at the University of Miami and at the Universities of Tokyo and Tohoku, in Japan, have discovered a spin battery effect: the ability to store energy into the magnetic spin of a material and to later extract that energy as electricity, without a chemical reaction. The researchers have built an actual device to demonstrate the effect that has a diameter about that of a human hair. This is a potentially game-changing discovery that could affect battery and other technologies. Quoting: Although the actual device... cannot even light up an LED..., the energy that might be stored in this way could potentially run a car for miles. The possibilities are endless, Barnes said.'"
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"Spin Battery" Effect Discovered

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  • Re:Achem (Score:5, Informative)

    by Hordeking (1237940) on Friday March 13, 2009 @10:37AM (#27181355)

    Magnetic shielding?

    A Faraday cage?

    Faraday cages don't stop magnetic fields.

    Even if you do stop the magnetic field (it can be done, but not with a Faraday cage), your battery would be inducing regular and eddy currents in the shield, which will convert the magnetic field to useless thermal energy over time.

  • by Scareduck (177470) on Friday March 13, 2009 @10:59AM (#27181681) Homepage Journal
    Here's the pre-publication link in Nature [nature.com].

    The electromotive force (e.m.f.) predicted by Faraday's law reflects the forces acting on the charge, â"e, of an electron moving through a device or circuit, and is proportional to the time derivative of the magnetic field. This conventional e.m.f. is usually absent for stationary circuits and static magnetic fields. There are also forces that act on the spin of an electron; it has been recently predicted that, for circuits that are in part composed of ferromagnetic materials, there arises an e.m.f. of spin origin even for a static magnetic field. This e.m.f. can be attributed to a time-varying magnetization of the host material, such as the motion of magnetic domains in a static magnetic field, and reflects the conversion of magnetic to electrical energy. Here we show that such an e.m.f. can indeed be induced by a static magnetic field in magnetic tunnel junctions containing zinc-blende-structured MnAs quantum nanomagnets. The observed e.m.f. operates on a timescale of approximately 10^2-10^3 seconds and results from the conversion of the magnetic energy of the superparamagnetic MnAs nanomagnets into electrical energy when these magnets undergo magnetic quantum tunnelling. As a consequence, a huge magnetoresistance of up to 100,000 per cent is observed for certain bias voltages. Our results strongly support the contention that, in magnetic nanostructures, Faraday's law of induction must be generalized to account for forces of purely spin origin. The huge magnetoresistance and e.m.f. may find potential applications in high sensitivity magnetic sensors, as well as in new active devices such as 'spin batteries'.

    Readers with subscriptions can see the whole paper.

  • Re:Achem (Score:5, Informative)

    by Comboman (895500) on Friday March 13, 2009 @11:17AM (#27182025)
    When did "In THIS house, we obey the laws of thermodynamics" turn into some goddamn meme

    Simpsons season 6, episode 21 ("The PTA Disbands").

  • by Gat0r30y (957941) on Friday March 13, 2009 @11:23AM (#27182115) Homepage Journal

    moving parts in computers (and apparently can act as a replacement for the transistor).

    I don't think this is a replacement for the transistor, there certainly wasn't any indication that these can perform any logic operations. A replacement for your hard drive, which besides the fan (which you will probably still need), is the moving parts of your computer. It remains to be seen whether this process could be useful at scale. You need billions of these little things, along with some method for reading and writing to each unit. The HDD industry has been working for years (still in R&D phase) on spintronics to store data, and there is still a long way to go. But there is indeed great promise in it as well.

  • Readers with subscriptions can also leak the whole paper.

  • Link to actual paper (Score:5, Informative)

    by Animats (122034) on Friday March 13, 2009 @12:16PM (#27182929) Homepage

    Bypassing the layers of blogs, here's the actual paper. [nature.com] But it costs $32 to read more than the abstract.

    This is an application of superparamagnetism. [wikipedia.org] Paramagnetism is ordinarily a weak phenomenon, but there are some new materials for which this effect is much stronger.

    It's too early to tell if this is useful. Right now, it's in the category of "minor development in materials science overpromoted as a major breakthrough". It might turn out to have some relevance to MRI imaging or disk drives, both of which rely on fine-scale magnetic effects.

  • Re:Achem (Score:3, Informative)

    by mbkennel (97636) on Friday March 13, 2009 @12:58PM (#27183559)

    "Which is how does a device that stores an electrical charge (a battery) via magnetism not go dead based simply on inductive coupling with nearby metals?"

    Firstly, inductive coupling requires time dependent magnetic fields and probably realistically macroscopically reinforcing ones so that the field strength is appreciable at a distance.

    And then it could be locally thermodynamically stable, like opposing domains on a ferromagnetic surface, like a hard drive.

    Hard drives wont to spontaneously erase themselves to 'all zero' over human lifetimes.

    The global lowest energy state is "all spins pointing the same way".

  • Re:Achem (Score:5, Informative)

    by angel'o'sphere (80593) on Friday March 13, 2009 @01:04PM (#27183657) Homepage Journal


    In THIS house, we obey the laws of thermodynamics.

    Like other posters pointed out: you likely don't know what thermodynamics even is. Hint: thermo has something to do with temperature. Thermodynamcs is about entropy and heat not about magnetic fields or electric fields.

    To your question:
    In other words -- what's preventing the battery from discharging?
    The battery does not discharge in the same way your hard drive is not losing its content just so. The magnetic fields in such a device are static that means they don't move, that means they don't induce anything to anything. However if you read the article (yes the linked article, you can read it, you know!!) you find that nanoscale areas are magnetized and that tunnel effects are involved. I guess that such small areas can "discharge" randomly vie tunnel effects (similar to radioactive decay).

    angel'o'sphere

  • Re:Why An LED... (Score:1, Informative)

    by Anonymous Coward on Friday March 13, 2009 @01:54PM (#27184379)

    What?

    LED's require very little "juice". The quote from wikipedia just means they don't handle fluctuations very well. i.e. if you don't give them a high enough voltage or give them too high a current they just don't work as efficiently.

    Here is another quote from the same f'n page: "LEDs produce more light per watt than incandescent bulbs." http://en.wikipedia.org/wiki/Led#Advantages [wikipedia.org]

  • by Anonymous Coward on Friday March 13, 2009 @02:19PM (#27184771)

    Ask and you shall receive...

    Electromotive force and huge magnetoresistance in magnetic tunnel junctions
    Pham Nam Hai1, Shinobu Ohya1,2, Masaaki Tanaka1,2, Stewart E. Barnes3,4 & Sadamichi Maekawa5,6

    Department of Electrical Engineering and Information Systems, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-8656, Japan
    Japan Science and Technology Agency, 4-1-8 Honcho, Kawaguchi-shi 332-0012, Japan
    Physics Department, University of Miami, Coral Gables, Florida 33124, USA
    TCM, Cavendish Laboratory, University of Cambridge, Cambridge CB3 0HE, UK
    Institute for Materials Research, Tohoku University, Sendai 980-8577, Japan
    CREST, Japan Science and Technology Agency, Tokyo 100-0075, Japan
    Correspondence to: Masaaki Tanaka1,2 Correspondence and requests for materials should be addressed to M.T. (Email: masaaki@ee.t.u-tokyo.ac.jp).

    The electromotive force (e.m.f.) predicted by Faraday's law reflects the forces acting on the charge, -e, of an electron moving through a device or circuit, and is proportional to the time derivative of the magnetic field. This conventional e.m.f. is usually absent for stationary circuits and static magnetic fields. There are also forces that act on the spin of an electron; it has been recently predicted1, 2 that, for circuits that are in part composed of ferromagnetic materials, there arises an e.m.f. of spin origin even for a static magnetic field. This e.m.f. can be attributed to a time-varying magnetization of the host material, such as the motion of magnetic domains in a static magnetic field, and reflects the conversion of magnetic to electrical energy. Here we show that such an e.m.f. can indeed be induced by a static magnetic field in magnetic tunnel junctions containing zinc-blende-structured MnAs quantum nanomagnets. The observed e.m.f. operates on a timescale of approximately 102-103 seconds and results from the conversion of the magnetic energy of the superparamagnetic MnAs nanomagnets into electrical energy when these magnets undergo magnetic quantum tunnelling. As a consequence, a huge magnetoresistance of up to 100,000 per cent is observed for certain bias voltages. Our results strongly support the contention that, in magnetic nanostructures, Faraday's law of induction must be generalized to account for forces of purely spin origin. The huge magnetoresistance and e.m.f. may find potential applications in high sensitivity magnetic sensors, as well as in new active devices such as 'spin batteries'.

    Three ingredients are important to the observation of a large spin-derived e.m.f. The first is an ensemble of superparamagnetic nanometre-sized magnets with a large spin S 200. Owing to a very large magnetic anisotropy, the magnetic moment is aligned along the z direction with a component Sz = S of the spin in this direction. A static magnetic field H = Hz splits these two ground states (with Sz = S) by an energy 2H = 2SgBH (where g is the g-factor and B is the Bohr magneton). It is this appreciable energy difference that drives the e.m.f. Second, these nanomagnets constitute an essential conductive path through our magnetic tunnel junctions (MTJs), but have such a small capacitance C that the Coulomb energy U = e2/(2C) for adding or removing electrons exceeds the thermal energy kBT, effectively blocking sequential electrical conduction3. However, as is commonplace, there are spin-flip channels of many-body origin that conduct under this 'Coulomb blockade'. Third, for a temperature T = 3 K, an S 200 nanomagnet would not usually relax within our ten-minute timescale. However, the spin-flip channels mix Sz = -S with -S+1 and ultimately the two ground states Sz = S. With the conduction of a single electron, relaxation -S S occurs, the electron gains an energy 2SgBH, and for an ensemble this results in a steady current driven by an e.m.f. = 2SgBH/e.

    Normally an MTJ consists of metallic thin-film ferromagnetic electrodes and a thin tunnel barrier made of an insulator. The MTJs in this study are unique (Fig. 1a); they co

  • by Anonymous Coward on Friday March 13, 2009 @03:34PM (#27185819)

    They'll never build skyscrapers out of synth spider silk because the wrong kind of strength is required. Silk's strength is pull strength like that of wire rope. But, for a skyscraper the strength required is compresion and torsion.

    But it would be nice to see a bridge made of a synth silk material

  • Re:Why An LED... (Score:3, Informative)

    by fatboy (6851) on Friday March 13, 2009 @03:45PM (#27185963)

    I don't know of any common light sources that are more efficient than LEDs.

    I don't think you understand the meaning of that Wikipedia quote.

    The Voltage "above the threshold" means the voltage to cause the NP junction to conduct. In most diodes, that is .7 volts.

    The part about "a current below the rating", means that if you present enough voltage across the PN junction, as to reach the current limit of the PN junction, it will fail.

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