When Mother Nature gets frustrated...
When you make a choice between two things, be it a place for your next vacation or a decision about your job, one part in you is satisfied while another is frustrated. The same phenomenon exists in nature, where this state of frustration is an important factor of interaction between complex systems. And this is one of the basis of a research project from physicists at Penn State University (PSU) about artificial 'spin ice.' Surprisingly enough, studying the interaction between hydrogen and oxygen atoms with this concept of frustration in mind might lead to advanced magnetic-recording devices and smaller hard drives.
Here is an explanation of this concept of frustration in nature, given by Peter Schiffer, professor at PSU.
Schiffer explains, for example, that neural networks, which allow the brain to function, and protein molecules, which allow living matter to function, consist of thousands to millions of interacting components, and that a crucial element of these interactions is that they often are "frustrated." "When two different and competing signals are sent in the brain, the brain needs to choose which signal will dominate in order to take a particular action," Schiffer says.
"Frustration happens even in a simple substance such as ice, which consists of only hydrogen and oxygen atoms, because there are competing forces on the hydrogen atoms pushing them between different positions relative to their neighboring oxygen atoms," he explains.
And this is why Sciffer, along with other professors at PSU, Vincent Crespi and Nitin Samarth, have decided to build "a magnetically frustrated material" made of microscopic bar magnets analogous to hydrogen atoms in ice.
Here is a magnetic-force microscope image (MFM) showing the magnetic moments of this artificial 'spin ice.' The peaks and valleys show the orientations of the magnetic moments (Credit: William McConville and Ruifang Wang, Penn State). Here is a link to a larger version.
Schiffer and his colleagues have developed a new method to study the subtleties of frustration, which involves using "electron beam lithography" to build a magnetically frustrated material by sculpting arrays of hundreds of thousands of microscopic bar magnets, each only a few millionths of an inch in size.
The samples were fabricated at the PSU Nanofabrication Facility by Penn State graduate student Ruifang Wang. "Rather than relying on chemically synthesized materials whose magnetic atoms are pre-arranged, we decided to make our own frustrated system," Samarth says.
For more information, this research work has been published by Nature under the name "Artificial 'spin ice' in a geometrically frustrated lattice of nanoscale ferromagnetic islands" (Volume 439, Number 7074, Pages 303-306, 19 January 19, 2006). Here are two links to the abstract and to the Editor's Summary. And thanks to arXiv.org, you can also read the full paper (PDF format, 13 pages, 295 KB).
And don't think that this research is over. These physicists are still investigating the nature of frustration in large natural networks and think their interacting magnets will be even more relevant to modern magnetic-recording technology.
Sources: Penn State University news release, January 18, 2006; and various web sites
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