Open a giant spin Seebeck effect



Researchers at Ohio State University have found a method that can radically enhance the spin Seebeck effect, which would increase the efficiency of generating electricity they developed a thermocouple is a million times.
 
Researchers from Ohio State University (USA) have found a method that can radically enhance the spin Seebeck effect, which would increase the efficiency of generating electricity they developed a thermocouple is a million times.

Seebeck effect, opened nearly 200 years ago, is an electromotive force (EMF) in a closed electrical circuit consisting of series-connected dissimilar conductors, contacts between them have different temperatures. It is important for space probes traveling to remote areas of the solar system and beyond, as well as for a variety of thermoelectric sensors. Recently, researchers from Ohio State University have found a method that can make one of the varieties of the Seebeck effect is radically more effective.



The main problem of the Seebeck effect that the temperature difference is observed in vivo, is too small to produce significant amounts of energy. There is a similar phenomenon spin Seebeck effect (SEZ), opened a few years ago. It magnesium metal, one end of which is cold, and the other - hot, is an analogue of the classical thermocouple Seebeck effect. However, American researchers have conceived something else: to create a free economic zone in the nonmagnetic semiconductor is placed in an external magnetic field (3 T) at temperatures ranging from 2 to 20 K (slightly warmer liquid hydrogen).

It was found that while there is, as the researchers dubbed it "a giant spin Seebeck effect" (GSEZ).

The name is not accidental. Usually degree temperature difference at the ends of the thermocouple latter produces several microvolts. And in case GSEZ - a few millivolts. But a thousand-fold increase in the voltage - is not everything. Power taken from the thermocouple allegedly scientists climbed a million times. As you guessed, before the end of the study the phenomenon team has applied for invention: too will differ strikingly new method for the generation of electricity on the temperature difference from the known thermocouple!


However, the theoretical basis of the new effect still remains a weak point. Simply put, the reasons for the enormous amplification of spin thermoelectric effects in the case of non-magnetic materials are unknown. The researchers only cautiously suggest that there is an extreme case of the phonon drag of electrons accompanying their extremely rapid movement between the ends of a thermocouple. As a result of collisions with electrons, phonons can carries them away, and at the cold end of the sample would be to accumulate a negative charge (at the hot - positive); this will take place as long as the potential difference arising balances the drag effect. This potential difference and is an important component of the thermoelectric power, which at low temperatures can be in the tens or hundreds of times higher than normal.

But here's the rub: the observed giant spin Seebeck effect gives millionokratnoe increase in the thermocouple EMF! Probably when phonons drag electrons properties of semiconductors causes electrons to spin, which stabilizes their trajectories. Very rough analogy such stabilization trajectories can be called twisting bullets in rifled firearms by rifling of the barrel, making it possible flight neoperёnnoy elongated bullets without tumbling.

While the new effect was registered only in indium antimonide doped not called developers substances. Alas, this is not the cheapest material, and an external magnetic field in which he worked, was 3 T (as in MRI apparatus), but the researchers note: there are no obstacles that do not allow to use the effect on other semiconductors, and even a few more high temperature.

The semiconductor base of new thermocouples can afford to use them in the form of plates in a variety of areas, ranging from pipe cooling systems and ending with a thermoelectric heat sink. In such "heat engines", as they call them pioneers GSEZ will not be moving parts, and their degradation will go no faster than conventional semiconductors in a stable mode. In other words, they will be able to work for decades. The relative cheapness of semiconductors can afford to use them even to feed their own computers from the heat, now useless scattered in space and reduces the efficiency of the computer itself.

Even in its current form, at low temperatures, a new kind of thermoelectric effect can be used in space: AMC work most of the time at temperatures below 20 K, and thermoelectric cooling would be useful to them.

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