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

More articles from Physics and Astronomy:

nachricht Shape matters when light meets atom
05.12.2016 | Centre for Quantum Technologies at the National University of Singapore

nachricht Climate cycles may explain how running water carved Mars' surface features
02.12.2016 | Penn State

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: Novel silicon etching technique crafts 3-D gradient refractive index micro-optics

A multi-institutional research collaboration has created a novel approach for fabricating three-dimensional micro-optics through the shape-defined formation of porous silicon (PSi), with broad impacts in integrated optoelectronics, imaging, and photovoltaics.

Working with colleagues at Stanford and The Dow Chemical Company, researchers at the University of Illinois at Urbana-Champaign fabricated 3-D birefringent...

Im Focus: Quantum Particles Form Droplets

In experiments with magnetic atoms conducted at extremely low temperatures, scientists have demonstrated a unique phase of matter: The atoms form a new type of quantum liquid or quantum droplet state. These so called quantum droplets may preserve their form in absence of external confinement because of quantum effects. The joint team of experimental physicists from Innsbruck and theoretical physicists from Hannover report on their findings in the journal Physical Review X.

“Our Quantum droplets are in the gas phase but they still drop like a rock,” explains experimental physicist Francesca Ferlaino when talking about the...

Im Focus: MADMAX: Max Planck Institute for Physics takes up axion research

The Max Planck Institute for Physics (MPP) is opening up a new research field. A workshop from November 21 - 22, 2016 will mark the start of activities for an innovative axion experiment. Axions are still only purely hypothetical particles. Their detection could solve two fundamental problems in particle physics: What dark matter consists of and why it has not yet been possible to directly observe a CP violation for the strong interaction.

The “MADMAX” project is the MPP’s commitment to axion research. Axions are so far only a theoretical prediction and are difficult to detect: on the one hand,...

Im Focus: Molecules change shape when wet

Broadband rotational spectroscopy unravels structural reshaping of isolated molecules in the gas phase to accommodate water

In two recent publications in the Journal of Chemical Physics and in the Journal of Physical Chemistry Letters, researchers around Melanie Schnell from the Max...

Im Focus: Fraunhofer ISE Develops Highly Compact, High Frequency DC/DC Converter for Aviation

The efficiency of power electronic systems is not solely dependent on electrical efficiency but also on weight, for example, in mobile systems. When the weight of relevant components and devices in airplanes, for instance, is reduced, fuel savings can be achieved and correspondingly greenhouse gas emissions decreased. New materials and components based on gallium nitride (GaN) can help to reduce weight and increase the efficiency. With these new materials, power electronic switches can be operated at higher switching frequency, resulting in higher power density and lower material costs.

Researchers at the Fraunhofer Institute for Solar Energy Systems ISE together with partners have investigated how these materials can be used to make power...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

ICTM Conference 2017: Production technology for turbomachine manufacturing of the future

16.11.2016 | Event News

Innovation Day Laser Technology – Laser Additive Manufacturing

01.11.2016 | Event News

#IC2S2: When Social Science meets Computer Science - GESIS will host the IC2S2 conference 2017

14.10.2016 | Event News

 
Latest News

Researchers uncover protein-based “cancer signature”

05.12.2016 | Life Sciences

The Nagoya Protocol Creates Disadvantages for Many Countries when Applied to Microorganisms

05.12.2016 | Life Sciences

UTSA study describes new minimally invasive device to treat cancer and other illnesses

02.12.2016 | Medical Engineering

VideoLinks
B2B-VideoLinks
More VideoLinks >>>