As the ever-increasing power of computer chips brings us closer and closer to the limits of silicon technology, many researchers are betting that the future will belong to 'spintronics': a nanoscale technology in which information is carried not by the electron's charge, but by the electron's intrinsic spin.
If a reliable way can be found to control and manipulate the spins, spintronic devices could offer much higher data processing speeds, lower electric consumption, and many other advantages over conventional chips.
Physicist, Boldizsar Janko and his colleagues at the University of Notre Dame believe they have found such a control technique. The idea is to create the device as a series of layers, each only a few dozen nanometers thick. At the base is a layer of diluted magnetic semiconductor. When gallium arsenide is doped with manganese atoms, for example, each manganese atom contributes an extra electron, and thus an extra electron spin. The result is a semiconductor that can be magnetised much like iron. An insulator material is then layered over the base, followed by a layer of superconducting material. Next, a magnetic field is applied perpendicularly. Due to the basic physics of superconductors, the field can make it through only by pinching itself down into an array of nanoscale flux tubes. That 'super-concentrates' the field inside each tube, so that it creates a spot of high-intensity magnetism on the semiconductor layer below, which, in turn, creates a patch of closely aligned electron spins. The resulting spin patches, one for each flux tube, are then available for encoding information.
The effect resembles what happens with sprinkled iron filings on a piece of paper, and a magnet underneath: the presence of the magnet (the flux tube) makes the iron filings (the spins) stand at attention. As the filings are manipulated by moving the magnet, one can manipulate the spins in this system by moving the flux tubes. For example, an electric current flowing through the superconductor will cause a given flux tube to move to one side (with the patch of spins underneath moving along with it), while a current flowing in the reverse direction will move it back to the other side.
Although the team has tested this approach so far only through computer simulations, experiments are now underway to demonstrate the technique in the laboratory. See http://nsfvideo.nomex.net/press_releases/overview.smi for an animation of the process.
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