How Spintronics Went from the Lab to the Ipod W

commentary How spintronics went from the lab to the iPod W. Patrick McCray The commercial success of products based on giant magnetoresistance is often cited as a reason for supporting basic physics research. The reality is more complex, given the range of bodies, including IBM and the US military, involved in developing new technologies based on this Nobel-prize-winning discovery. n 1988, Albert Fert and Peter Grünberg independently discovered that the Ielectrical resistance of structures made of alternating layers of magnetic and non-magnetic metals can change by an unexpectedly large amount in the presence of an applied magnetic field. Within a decade, this seemingly esoteric observation had revolutionized the electronics industry by allowing hard drives to store ever- increasing amounts of data. And when Fert and Grünberg shared the Nobel Prize in Physics in 2007 for the discovery of S giant magnetoresistance (GMR), the Royal e Swedish Academy of Sciences announced IMAG that “GMR technology may also be regarded Y as one of the first major applications of the nanotechnology that is now so popular in a AFP / Gett very diverse range of fields.” (ref. 1). © However, the discovery of GMR is interesting for reasons beyond its Peter Grünberg (left) and Albert Fert discuss their Nobel-Prize-winning discovery of giant ‘nano-ness’. The story of GMR raises a magnetoresistance with the press in 2007. number of questions about the nature of contemporary knowledge production2. Does the venerable linear model3,4 — with basic be exploited in read heads for magnetic Although the French team coined the research leading to applications — apply disks and sensors for detecting magnetic term ‘giant magnetoresistance’, it was to nanoscience and technology? Or, as fields. However, that all changed with the Grünberg who recognized that this effect some have argued, is nanotechnology an discovery of GMR in 1988. could be used to detect faint magnetic fields, example of ‘post-academic’ science, funded Grünberg and his team at the Jülich so he filed for a patent as his group wrote up by governments and corporations to solve Research Center in Germany made their its results. However, the two group leaders specific problems rather than advancing discovery — a change of about 10% in agreed to share the credit for the discovery knowledge for the sake of knowledge?5,6 electrical resistance in the presence of a (see Box 1). GMR also represented the first magnetic field — in a structure containing example of a new kind of technology called Discovery and commercialization a 1-nm thick layer of chromium (which is ‘spintronics’, so-called because it exploits Magnetoresistance, a change in the not magnetic) sandwiched between two the spin of the electron, as well as its electric electrical resistance of a conductor caused thicker layers of iron (which is magnetic)7. charge, to store and process information. by an applied magnetic field, was first Meanwhile Fert and co-workers at the Engineers first used GMR in niche observed by the physicist William Thomson University of Paris-Sud and Thomson CSF applications, such as sensors to detect very (Lord Kelvin) in 1857, wheras the physics observed an even larger effect (a change weak magnetic fields, but other companies underlying electron spin — which is the of about 50%) in more complex structures were eager to apply it in bigger and more ultimate source of magnetism in most containing about 60 alternating layers of lucrative markets. In particular, Stuart materials — dates back to the work of chromium and iron8. Both teams used Parkin and colleagues at IBM’s Almaden Paul Dirac, Wolfgang Pauli and others in molecular beam epitaxy (MBE), a central laboratory near San Jose exploited GMR the golden era of quantum mechanics. if often-overlooked research tool in the to make read heads that allowed magnetic The effect was quite small, typically a few history of nanotechnology9, to make their disc drives to become smaller while holding percent, but it was still large enough to multilayer samples. eight times more data than before, an 2 nature nanotechnology | VOL 4 | JANUARY 2009 | www.nature.com/naturenanotechnology © 2009 Macmillan Publishers Limited. All rights reserved commentary achievement that was reported on the front dollars. I said, I’m going to replace this with replacement technology was unknown, and page of The Wall Street Journal in November a fifty-cent chip.” without investment in new technologies for 1997 (ref. 10). A central part of Parkin’s Over the next decade, DARPA provided the computer and semiconductor industries, work was to show that GMR devices could tens of millions of dollars to support a economic competitiveness could suffer. be produced by ‘sputtering’, which was modestly sized international research Scientists, engineers and policy makers much faster than MBE, and some observers community made up of university-based in the United States all interpreted the wondered why he did not share the Nobel researchers, scientists from government commercialization of GMR as a sign that Prize with Fert and Grünberg11–13. laboratories and representatives from investment in nanotechnology was both These developments helped set the the electronics industry, most of whom sensible and prescient. Consequently, stage for the subsequent explosion in attended an annual DARPA meeting nanoelectronics — along with novel computer memory that, in turn, helped on spintronics. This community materials and new technologies for health, make it possible to store gigabytes of music, included physicists (both theoretical energy and biological applications — photos, videos and so forth on iPods and and experimental), materials scientists, became a “priority research area” in the other portable gadgets. These innovations chemists and engineers. initial formulation of the NNI (see, for prompted a member of the Nobel physics example, ref. 17). committee to comment that “you would not GMR also represented the Research initiatives in Europe and have an iPod without this [GMR] effect.” first example of a new kind of Asia took similar paths. The resulting (ref. 14). IBM’s GMR-based innovation flood of money for research transformed brought the broader field of spintronics to technology called ‘spintronics’ nanotechnology into one of the most a market worth billions of dollars per year robustly funded, aggressively pursued and (although the first iPods — introduced by The interest and support that DARPA widely promoted research areas in modern Apple in 2001 — actually used GMR-based and companies like IBM gave to researchers science and engineering. hard drives made by Toshiba.) interested in spintronics coincided with a larger movement underway in the United reflections Seizing an opportunity States and other countries to generate Debates about the nature of nanoscience, As actual products exploiting the GMR political support for a broader research- with its emphasis on applications rather than effect appeared on the market and and-development effort in nanotechnology. discovery, have suggested that it is one of the more scientists began to do research in Advocates of national policies to support first fully realized examples of post-academic spintronics15, science managers from nanotechnology used the economic science6. However, others cite GMR-based military laboratories and funding agencies importance of nanoelectronics, and the hard drives as an example of the commercial began to take notice. The Defense Advanced commercial success of spintronics in benefits that follow from support for basic Research Projects Agency (DARPA) was one particular, to support this broader agenda research and of the importance of funding of GMR’s first champions. Founded in the (see, for example, ref. 16). the best science and scientists rather than wake of Sputnik, DARPA had a reputation In the US, for instance, nanoelectronics research that is expected to deliver economic among scientists as lean, agile and able figured prominently in the discussions returns4. In the most basic form of this so- to direct considerable resources to high- between scientists and funding agencies called ‘linear model’ of research (presented risk, high-payoff technologies. During the that led to the establishment of the most famously in a report called Science, 1990s, DARPA invested millions of dollars National Nanotechnology Initiative The Endless Frontier 3 that was prepared into university-based spintronics research, (NNI). In 1997 and 1998, the National for the US president by Vannevar Bush in funding fundamental and applied projects. Science Foundation (NSF) organized 1945) there is a direct path from scientific Stuart A. Wolf, a physicist at the Naval studies to evaluate possible opportunities discovery to application. Research Laboratory in Washington, DC, in nanotechnology, and a standard case Historians, of course, recognize that was the main champion for spintronics and for supporting nanotechnology started ‘pure science’ is very much a social other GMR-based research programmes at to emerge: some time in the next ten-to- construction and one that often, after DARPA. One technology he was especially fifteen years the semiconductor industry closer scrutiny, may not be quite so interested in was magnetic random-access will encounter serious technical problems unfettered as it seems at first. However, memory (MRAM). Like GMR-enabled in its effort to improve the performance of as recent sociological and historical disk drives, MRAM is based on metallic devices

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