Magnetic RAM could soon absorb and use waste heat

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Here’s an interesting one that we’re still trying to get our heads around: Researchers at the Physical and Technical Institute (PTB) in Braunschweig, Germany have discovered that heat — waste heat — can be used to control computer circuits. This technique could be used to make digital components that switch faster or store data more efficiently, but more importantly it provides an electronic way of controlling thermal currents in a computer system.
This effect doesn’t apply to silicon transistors, but rather to magnetic tunnel structures — the magnetic switches that are already commercially found in MRAM (magnetic RAM) and on hard drive heads. In these tunnel structures, two pieces of magnetic material are sandwiched together, separated by a 1nm-thick insulator (below right). If the two poles have the same magnetization, current flows readily across the switch, and if they are opposed, resistance is much higher. In other words, by switching the magnetization of one of the poles, you can store a single bit of non-volatile data.
Now, the researchers at PTB have discovered that not only does the magnetization affect the flow of electricity, but also the flow of heat. When the two poles of the switch have the same magnetization, heat flows more readily across, and vice versa. This is significant because of the thermoelectric effect. Basically, waste heat can be used to heat one side of the magnetic switch, thus creating an electrical potential between the hot and cold ends. Then, by flipping the switch (making sure the magnetic moment from both ends match), a thermoelectric voltage would flow across — and at the same time, thanks to the conservation of energy, you would also be controlling the thermal current and consuming waste heat.
As for actual applications of the technology, which is technically called “tunnel magneto thermoelectric voltage” and is part of the spintronics school of research, in case you were wondering, we’re most likely a few years out from MRAM that can suck up your computer’s waste heat. Imagine the possibilities in mobile computing, though, or in data centers where one of the largest running costs is air conditioning.

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