Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

50-year-old magnetic mystery solved; quantum structure obeys classical physics

07.01.2004


Ohio State University physicists and their colleagues have demonstrated for the first time a type of magnetic behavior that was predicted to exist more than 50 years ago.

The behavior involves a special kind of energy transition among atoms in a very small magnet, called chromium-8 (Cr8). And while scientists have long thought that the effect was controlled purely by quantum mechanics, the magnet’s behavior appears to reflect the laws of classical physics.

The classical laws of movement and energy are ones that people experience in daily life, and they normally only apply to objects that are large enough to be seen with the naked eye. In contrast, the molecular magnet Cr8 is so small that quantum mechanics -- the science that describes the interactions of subatomic particles -- should rule its behavior.



The finding could help bridge the gap between quantum and classical approaches for understanding these tiny structures, and aid the future development of useful devices based on nanotechnology, such as very powerful, very small computers.

“This shows that we can understand important aspects of quantum behavior with classical thinking,” said Oliver Waldmann, a visiting scientist in the Department of Physics at Ohio State. “That’s a twist that I like.”

Waldmann and his colleagues published their results in a recent issue of the journal Physical Review Letters.

Materials such as Cr8 are called molecular magnets, because they are composed of only a small number of atoms that form a large molecule. The spins of the atoms’ electrons provide the magnetism, and the molecule itself acts as separate magnet.

In the case of Cr8, the structure contains eight electrically charged chromium atoms linked in a ring that measures less than one nanometer, or billionth of a meter, across.

The spins of four of the chromium atoms are magnetized in one direction -- spin-up -- and the other four in the opposite direction -- spin-down.

The opposite spins cancel each other out, making Cr8 what’s known as an antiferromagnet. Researchers call the up-and-down spin structure a Néel structure, after the late French physicist Louis Néel, who in 1970 won the Nobel Prize for his discovery of antiferromagnetism.

In 1952, Princeton University physicist and Nobelist Philip W. Anderson predicted that when the atoms in an antiferromagnet become slightly canted out of their straight spin-up and spin-down positions, their energy transitions take on a wavelike structure.

But Anderson’s theory suggests that the magnet will generate a second kind of excitation called the Néel excitation when the electrons in its atoms are at their lowest possible energy state. This kind of Néel excitation has not been demonstrated, until now.

Waldmann performed the theoretical work that underpinned the experiment while he was at the University Erlangen-Nuremberg in Germany, and colleagues in Europe performed the experiment. Waldmann recently analyzed the data while working with Arthur J. Epstein, Distinguished University Professor of physics and chemistry at Ohio State.

To Epstein, the study demonstrates that magnets based on molecules with special internal molecular structures can produce new phenomena, such as Waldmann’s observation of the Néel excitation.

He added that using molecular magnets gives scientists the opportunity to use synthetic chemistry to tune magnetic properties, and introduce previously unknown properties into magnets.

“This enables both new fundamental science and new potential technologies,” Epstein said.

The scientists cooled a sample of Cr8 to only a few degrees Kelvin -- colder than minus 450 degrees F -- to lower the energy levels of electrons in the atoms as much as possible. Then they bombarded the material with neutrons to energize the electrons just enough for them to display Néel excitation.

The experiment was a tricky one, Waldmann said. Atoms sometimes absorb the neutrons, which would weaken signals from low-energy effects such as the Néel excitation.

The physicists chose Cr8 because the material would produce stronger signals, he said.

When Waldmann analyzed the spectrum of energy levels detected during the experiment, he saw that it matched the levels that were predicted by Anderson’s theory half a century ago.

“The pieces just fell into place,” Waldmann said. “Of course, I’d hoped for a long time that we would see the Néel excitation -- we started this project four years ago -- but when it actually happened, it was still a surprise.”

The find is more surprising still, given that the Néel excitation is a quantum mechanical effect, and the physicists could explain its properties using a classical approach.

That idea could bode well for experts who believe that quantum mechanical effects can be exploited to create a new kind of electronics.

Normal electronics encode computer data based on a binary code of ones and zeros, depending on the presence or absence of an electron within a material such as silicon. But in principle, the direction of a spinning electron -- either “spin up” or “spin down” -- can be used as data, too. And other directions of spin in-between up and down could theoretically provide further information, so a single electron could store many different pieces of data.

Such quantum computers could be much smaller than traditional electronics, and much more powerful. Instead of silicon chips, they would be built from arrays of tiny molecular structures similar to Cr8.

But working devices based on this technology could be decades away, and Waldmann said his work is only a basic step in that direction.

“Our work shows that these excitations can be understood with very basic reasoning, and this surely will help us to understand other effects that can be observed in such materials,” he said.

Co-authors on the Physical Review Letters paper include Tatiana Guidi of the Università Politecnica delle Marche in Italy; Stefano Carretta of the Università di Parma, also in Italy; Claudia Mondelli at the Institut Laue-Langevin in France; and Angela Dearden at the University of Manchester in the UK.

#

Contact: Oliver Waldmann, (614) 292-3705; Waldmann.1@osu.edu
Arthur J. Epstein, (614) 292-1133; Epstein.2@osu.edu
Written by Pam Frost Gorder, (614) 292-9475; Gorder.1@osu.edu

Pam Frost Gorder | OSU
Further information:
http://researchnews.osu.edu/archive/neelwave.htm

More articles from Physics and Astronomy:

nachricht Studying fundamental particles in materials
17.01.2017 | Max-Planck-Institut für Struktur und Dynamik der Materie

nachricht Seeing the quantum future... literally
16.01.2017 | University of Sydney

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: Interfacial Superconductivity: Magnetic and superconducting order revealed simultaneously

Researchers from the University of Hamburg in Germany, in collaboration with colleagues from the University of Aarhus in Denmark, have synthesized a new superconducting material by growing a few layers of an antiferromagnetic transition-metal chalcogenide on a bismuth-based topological insulator, both being non-superconducting materials.

While superconductivity and magnetism are generally believed to be mutually exclusive, surprisingly, in this new material, superconducting correlations...

Im Focus: Studying fundamental particles in materials

Laser-driving of semimetals allows creating novel quasiparticle states within condensed matter systems and switching between different states on ultrafast time scales

Studying properties of fundamental particles in condensed matter systems is a promising approach to quantum field theory. Quasiparticles offer the opportunity...

Im Focus: Designing Architecture with Solar Building Envelopes

Among the general public, solar thermal energy is currently associated with dark blue, rectangular collectors on building roofs. Technologies are needed for aesthetically high quality architecture which offer the architect more room for manoeuvre when it comes to low- and plus-energy buildings. With the “ArKol” project, researchers at Fraunhofer ISE together with partners are currently developing two façade collectors for solar thermal energy generation, which permit a high degree of design flexibility: a strip collector for opaque façade sections and a solar thermal blind for transparent sections. The current state of the two developments will be presented at the BAU 2017 trade fair.

As part of the “ArKol – development of architecturally highly integrated façade collectors with heat pipes” project, Fraunhofer ISE together with its partners...

Im Focus: How to inflate a hardened concrete shell with a weight of 80 t

At TU Wien, an alternative for resource intensive formwork for the construction of concrete domes was developed. It is now used in a test dome for the Austrian Federal Railways Infrastructure (ÖBB Infrastruktur).

Concrete shells are efficient structures, but not very resource efficient. The formwork for the construction of concrete domes alone requires a high amount of...

Im Focus: Bacterial Pac Man molecule snaps at sugar

Many pathogens use certain sugar compounds from their host to help conceal themselves against the immune system. Scientists at the University of Bonn have now, in cooperation with researchers at the University of York in the United Kingdom, analyzed the dynamics of a bacterial molecule that is involved in this process. They demonstrate that the protein grabs onto the sugar molecule with a Pac Man-like chewing motion and holds it until it can be used. Their results could help design therapeutics that could make the protein poorer at grabbing and holding and hence compromise the pathogen in the host. The study has now been published in “Biophysical Journal”.

The cells of the mouth, nose and intestinal mucosa produce large quantities of a chemical called sialic acid. Many bacteria possess a special transport system...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

12V, 48V, high-voltage – trends in E/E automotive architecture

10.01.2017 | Event News

2nd Conference on Non-Textual Information on 10 and 11 May 2017 in Hannover

09.01.2017 | Event News

Nothing will happen without batteries making it happen!

05.01.2017 | Event News

 
Latest News

Water - as the underlying driver of the Earth’s carbon cycle

17.01.2017 | Earth Sciences

Interfacial Superconductivity: Magnetic and superconducting order revealed simultaneously

17.01.2017 | Materials Sciences

Smart homes will “LISTEN” to your voice

17.01.2017 | Architecture and Construction

VideoLinks
B2B-VideoLinks
More VideoLinks >>>