Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

Suddenly Magnetic

10.04.2013
It came as a surprise: If tin atoms are arranged on a silicon substrate in a special way, the material becomes magnetic. University of Würzburg physicists have successfully conducted such an experiment. This research might open up a new way of processing information.
Take a small, thin silicon disk and deposit tin atoms on its surface in a regular pattern. Although both starting materials do not possess any magnetic properties, their combination induces a magnetic state – a surprising result. University of Würzburg physicists have succeeded in producing this effect experimentally. Their research is reported in the current issue of the prestigious journal Nature Communications.

Regular patterns make it possible

According to Dr. Jörg Schäfer, the unexpected magnetism is attributable to "regularly ordered patterns of electron spin". Schäfer is a private lecturer at the Department for Experimental Physics IV of the University of Würzburg. Working in the study group of Professor Ralph Claessen, who heads the department, he was in charge of the decisive experiments; the theoretical simulation was conducted at the Department for Theoretical Physics I, headed by Professor Werner Hanke.

Spin: It is the intrinsic angular momentum of electrons. Electrons are electrically charged so that this rotation automatically creates a magnetic field. Thus, they are like tiny magnets. As a rule, however, this has no consequences: The enormous number of electrons that are present even in minute quantities of a substance and the fact that these "electron magnets" point randomly in all directions cause them to cancel out as a whole.

When atoms sense each other

The magnetic properties found by the Würzburg physicists in their experiments are due to a special reason: "The clever arrangement of individually deposited metal atoms gives rise to regularly ordered patterns of electron spin," Jörg Schäfer explains. After adsorption on the silicon substrate, each atom only possessed one electron together with its spin in the outermost orbital – a so-called valence electron. Such electrons were able to get in contact with a neighboring atom, which process can be pictured as electron hopping between the atoms. Only then is it possible for the electron spins to sense each other in their various positions and to align themselves accordingly.

However, there was yet another mystery for the physicists to solve: The metal atoms arranged themselves on the silicon substrate at evenly spaced distances in what is called a "triangular lattice" as the scientists found out in their experiments.

The problem of frustration

The problem: Nature tends to prefer a spin arrangement in which the spins of neighboring positions point in opposite directions," says Jörg Schäfer. But how is this supposed to work in a triangle – which spin should the third partner anti-align with? A seemingly insolvable problem, for which reason it is known as the "problem of frustration" in physics. After thorough examination, the scientists were able to determine how the problem was solved in their experiment: "The spins of the tin atoms arranged themselves on the silicon substrate in an unusual pattern with row-wise alternating spin orientation," Schäfer explains (see illustration).

According to Schäfer, this discovery of magnetic order essentially illustrates the astonishing possibilities opening up for the control of electrical interactions on an atomic scale. Our study thus suggests an approach for the implementation of spin-based information processing on the basis of well-established semiconductor materials, such as silicon, where the data are magnetically coded.

Close collaboration between theoretical and experimental physicists

The experiment of the Würzburg researchers was conducted within the DFG-funded research unit FOR 1162 "Electron Correlation-Induced Phenomena in Surfaces and Interfaces with Tunable Interactions". The project involved a close collaboration between theoretical and experimental physicists: The atom lattice and the hopping processes of the electrons were modeled in complex computer simulations at the Department for Theoretical Physics I. The experiments were conducted at the Department for Experimental Physics IV.

The physicists gained insight into the spin arrangement by means of photoelectron spectroscopy. In this method, the ejection of electrons from the surface of a sample is induced by exposure to X-ray radiation and the properties of the emitted electrons are then analyzed. The required information on the magnetic order can be derived from their energy distribution and angular distribution," says Schäfer. Their behavior was also modeled in parallel in so-called many body calculations, where the spin pattern was directly factored in.

Both methods are in agreement with respect to the electron signals

The results of both variants surprised the scientists: Both methods showed corresponding patterns of signal intensity caused by a periodic spin arrangement. "A surprising result" in Schäfer's opinion – especially considering that only non-magnetic components were used in the experiment.

“Magnetic order in a frustrated two-dimensional atom lattice at a semiconductor surface”. Gang Li, Philipp Höpfner, Jörg Schäfer, Sebastian Meyer, Aaron Bostwick, Eli Rotenberg, Ralph Claessen, Werner Hanke. Nature Communications, DOI: 10.1038/ncomms2617

Contact person

Prof. Dr. Werner Hanke, T: +49 (0)931 31-85714,
hanke@physik.uni-wuerzburg.de

Prof. Dr. Ralph Claessen, T: +49 (0) 931 31-85732,
claessen@physik.uni-wuerzburg.de

PD Dr. Jörg Schäfer, T: +49 (0)931 31-83483,
joerg.schaefer@physik.uni-wuerzburg.de

Gunnar Bartsch | Uni Würzburg
Further information:
http://www.uni-wuerzburg.de

All articles from Physics and Astronomy >>>

The most recent press releases about innovation >>>

Die letzten 5 Focus-News des innovations-reports im Überblick:

Im Focus: New proton record: Researchers measure magnetic moment with greatest possible precision

High-precision measurement of the g-factor eleven times more precise than before / Results indicate a strong similarity between protons and antiprotons

The magnetic moment of an individual proton is inconceivably small, but can still be quantified. The basis for undertaking this measurement was laid over ten...

Im Focus: Frictional Heat Powers Hydrothermal Activity on Enceladus

Computer simulation shows how the icy moon heats water in a porous rock core

Heat from the friction of rocks caused by tidal forces could be the “engine” for the hydrothermal activity on Saturn's moon Enceladus. This presupposes that...

Im Focus: Nanoparticles help with malaria diagnosis – new rapid test in development

The WHO reports an estimated 429,000 malaria deaths each year. The disease mostly affects tropical and subtropical regions and in particular the African continent. The Fraunhofer Institute for Silicate Research ISC teamed up with the Fraunhofer Institute for Molecular Biology and Applied Ecology IME and the Institute of Tropical Medicine at the University of Tübingen for a new test method to detect malaria parasites in blood. The idea of the research project “NanoFRET” is to develop a highly sensitive and reliable rapid diagnostic test so that patient treatment can begin as early as possible.

Malaria is caused by parasites transmitted by mosquito bite. The most dangerous form of malaria is malaria tropica. Left untreated, it is fatal in most cases....

Im Focus: A “cosmic snake” reveals the structure of remote galaxies

The formation of stars in distant galaxies is still largely unexplored. For the first time, astron-omers at the University of Geneva have now been able to closely observe a star system six billion light-years away. In doing so, they are confirming earlier simulations made by the University of Zurich. One special effect is made possible by the multiple reflections of images that run through the cosmos like a snake.

Today, astronomers have a pretty accurate idea of how stars were formed in the recent cosmic past. But do these laws also apply to older galaxies? For around a...

Im Focus: Visual intelligence is not the same as IQ

Just because someone is smart and well-motivated doesn't mean he or she can learn the visual skills needed to excel at tasks like matching fingerprints, interpreting medical X-rays, keeping track of aircraft on radar displays or forensic face matching.

That is the implication of a new study which shows for the first time that there is a broad range of differences in people's visual ability and that these...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

Ecology Across Borders: International conference brings together 1,500 ecologists

15.11.2017 | Event News

Road into laboratory: Users discuss biaxial fatigue-testing for car and truck wheel

15.11.2017 | Event News

#Berlin5GWeek: The right network for Industry 4.0

30.10.2017 | Event News

 
Latest News

IceCube experiment finds Earth can block high-energy particles from nuclear reactions

24.11.2017 | Physics and Astronomy

A 'half-hearted' solution to one-sided heart failure

24.11.2017 | Health and Medicine

Heidelberg Researchers Study Unique Underwater Stalactites

24.11.2017 | Earth Sciences

VideoLinks
B2B-VideoLinks
More VideoLinks >>>