Spintronics - some important concepts

Last time, we introduced the concept of spintronics - manipulating spins of individual electrons for applications in memory storage and quantum computing. Today, we take a more detailed look at the physics concepts and material properties involved in spintronics. Science published a great review article about this topic in 2001, available at http://www.dtic.mil/cgi-bin/GetTRDoc?AD=ADA516289. 

Here are some concepts discussed in the article that you might like some additional resources to learn about:

Giant Magnetoresistance (GMR): Magnetoresistance (giant or small) is when a material's electrical resistance increases when the current runs parallel to an applied magnetic field. Magnetoresistance can therefore be used to interface with magnetic storage devices, but ordinary-sized magnetoresistance isn't strong enough to do the job. GMR, on the other hand, employs quantum mechanical concepts to introduce a large change in resistance, such that the resistance change can be used to read information stored in magnetic memory.

Ferromagnets: In elementary school, you might have learned to call these "permanent magnets"--materials that retain their magnetization even when there's no external magnetic field to keep all the spins in the same direction. But ferromagnets do have a weakness; if you heat them beyond their Curie temperature, they'll lose their magnetic ordering! So, when we design magnetic storage devices, it's important to know how hot they can get!

Semiconductors: On first pass, a semiconducting material is a pretty straightforward concept: It has a resistivity somewhere between the high resistivity of an insulator (letting no electrons through) and the low resistivity of a metal (letting all the electrons through). The reason a semiconductor behaves this way, though, is that its electronic band structure (the configuration of quantum states that the electrons are allowed to be in) has a small gap that can be easily manipulated:

Image credit:
 http://upload.wikimedia.org/wikipedia/commons/thumb/0/0b/Band_gap_comparison.svg/350px-Band_gap_comparison.svg.png

If you found the article above interesting, check out these even deeper (i.e., lengthier) reviews at http://arxiv.org/pdf/cond-mat/0405528.pdf, http://arxiv.org/ftp/arxiv/papers/0711/0711.1461.pdf, and http://arxiv.org/pdf/0801.0145v1.pdf.