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Spintronics May Lead to Quantum Microchips
Rashan writes "A Scientific American article which waxes poetic about the possibility of microchips which use the "spin" of an electron to perform their functions." An excellent explanation of a complex subject.
Those of you who are interested in the future of alternative computing, including quantum computing, might want to check out Caltech's Computing Beyond Silicon Summer School program. The top minds from around the world will present the latest information about quantum, molecular, and DNA computing.
Pun not intended.
Noticed something in that article - they state that the hard disk read heads use GMR sensors - not quite accurate. They use a single unit spin valve. GMR devices consist of many layers stacked on top of each other, and, more pertinantly, they operate at large magnetic fields. The sensor used have a lower field for peak sensitivity, and the change in resistance in smaller. GMR is conventionally used in the literature to indicate large, multi-layer devices. [0]
One thing that the article glosses over slightly is the difficulty in construction. Well, it's not so much a dificulty, as a paradigm shift. The metal GMR structures are built vertically onto a substrate, and thus the working current flows perpindicular to the plane of the substrate. This is distinct from traditional semiconductors, where the principle direction of the working current is parrallel to the plane of the substrate.
The notable exception would be the spin FET, but they've not actually been built yet, so it's a little tricky to comment on.
One option that the article didn't mention is the possibily of generating a magnetic semi-comductor / metal by using a conventional magnetic insulator (such as NiO, MnO or Fe2O3), and dopeing, or otherwise adjusting the electrical properties [1].
My research is into combined ab initio and statistical mechanical models of ultra thin films of the magnetic insulators. Particularly interesting is what happens when a two atom thick layer of iron is put over an NiO surface - spin dependant electron transfer, which is interesting. All in all, most of my work is the blue sky / basic building block level.
My point is that the spintronic devices require a finre degree of control in construction - by thier nature, the magnetic structure is important. Oh, and as a kicker to this, the length scale for a defect in a magnetic lattice is around 20 or so times larger than it's affect on the electrical properties. Additionally, it seems likely (to me) that other routes to mass manufacture may have to be found.
In other words: These are going to cost more. Not just because they are new, but also because they are inherently more complicated devices that electronic semiconductore devices.
[0] Well, in PhysRev anyway. IEEE and similar may use a different nomenclature
[1] My calculations suggest that a layer of NiO 4 formula units thick, or thinner, will be a metal.
The transition from laboratory discovery to actual heavy industry usage of GMR-based devices in the recording industry has been incredibly fast. One of the only other technologies that has transferred this quickly from lab to industry was the transistor, and it is obvious how influential and revolutionary transistors were. This gives a brief indication of the relative influence spintronics may have on the industry.
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