"Spin Battery" Effect Discovered

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.'"

Comments

Re:Achem

[Hordeking]

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.

The Nature pre-publication link

[Scareduck]

Here's the pre-publication link in Nature .

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:The Nature pre-publication link

[geekoid]

Readers with subscriptions can also leak the whole paper.

Re:The Nature pre-publication link

[Anonymous Coward]

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

Re:Achem

[Comboman]

When did "In THIS house, we obey the laws of thermodynamics" turn into some goddamn meme

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

Link to actual paper

[Animats]

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

This is an application of superparamagnetism. 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

[angel'o'sphere]

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