A new way in which magnetism and electric polarization are coupled has been discovered in CuFeO2

Feb 22, 2013
Structure of CuFeO2. The magnetism of the iron atoms (brown, with green arrows showing magnetism) influences the chemical bonds with the other elements (blue: copper, red: oxygen) to create a ferroelectric polarization (purple arrow P). Credit: 2012 The American Physical Society

Magnetism and electricity are two of the fundamental forces of nature. Combining them in a single multiferroic material in which one controls the other is not only of basic interest, but also relevant for practical applications. "Multiferroic materials can be used as magnetic sensors that change the sign of their electric polarization with a small magnetic field," says Yoshikazu Tanaka from the RIKEN SPring-8 Center in Harima. After studying the properties of the multiferroic CuFeO2, Tanaka and his colleagues have been able to verify a new mechanism by which magnetism and electricity can be coupled in a single material.

There are different ways in which magnetism and electric polarization, so-called ferroelectricity, are coupled in multiferroics. An understanding of these effects is important, because not only are multiferroics quite rare, but a better understanding of their properties might also help to develop materials where these effects are suitably strong for applications.

The researchers studied the magnetic properties of CuFeO2 using a beam of x-rays from the synchrotron facility at the SPring-8 Center. The x-rays specifically probe the electronic states of the in the crystal that are related to its magnetic properties, and the experiments reveal that these electronic states extend throughout the material in a periodic manner. This arrangement is directly responsible for the multiferroic properties, as it breaks the crystal symmetry and leads to a shift of the electrically charged atoms in the crystal.

At room temperature, each of the iron atoms is surrounded by a symmetric arrangement of and the magnetic moments of the are in disorder. However, at low temperatures the magnetic moments assume the shape of a screw (Fig. 1). Each magnetic moment slightly alters the energy of the in the crystal, depending on the relative orientation between the chemical bond direction and the magnetic moment. The resulting force then distorts the crystal structure and leads to an .

Although such a coupling model between magnetism and ferroelectricity has been proposed theoretically, this work represents the first experimental evidence for this particular mechanism. Moreover, although the practical applications for CuFeO2 itself are limited owing to the low temperatures at which this coupling occurs, the discovery could also guide the demonstration of similar materials which do have practical applications, explains Tanaka. "In future, this may lead to the discovery of other materials based on the same mechanism that work at room temperature."

Explore further: Pseudoparticles travel through photoactive material

More information: Tanaka, Y., et al. Incommensurate orbital modulation behind ferroelectricity in CuFeO2. Physical Review Letters 109, 127205 (2012). prl.aps.org/abstract/PRL/v109/i12/e127205

Related Stories

Fridge magnet transformed

Mar 11, 2011

The ubiquitous and unremarkable magnet, BaFe12O19, is manufactured in large volumes, has the simplest crystal structure in its class, and is often seen on refrigerator doors—but it is set for an inte ...

Recommended for you

Pseudoparticles travel through photoactive material

Apr 23, 2015

Researchers of Karlsruhe Institute of Technology (KIT) have unveiled an important step in the conversion of light into storable energy: Together with scientists of the Fritz Haber Institute in Berlin and ...

From metal to insulator and back again

Apr 22, 2015

New work from Carnegie's Russell Hemley and Ivan Naumov hones in on the physics underlying the recently discovered fact that some metals stop being metallic under pressure. Their work is published in Physical Re ...

Electron spin brings order to high entropy alloys

Apr 22, 2015

Researchers from North Carolina State University have discovered that electron spin brings a previously unknown degree of order to the high entropy alloy nickel iron chromium cobalt (NiFeCrCo) - and may play ...

Expanding the reach of metallic glass

Apr 22, 2015

Metallic glass, a class of materials that offers both pliability and strength, is poised for a friendly takeover of the chemical landscape.

Electrons move like light in three-dimensional solid

Apr 22, 2015

Electrons were observed to travel in a solid at an unusually high velocity, which remained the same independent of the electron energy. This anomalous light-like behavior is found in special two-dimensional ...

User comments : 2

Adjust slider to filter visible comments by rank

Display comments: newest first

Macksb
1 / 5 (1) Feb 22, 2013
This is another example of Art Winfree's theory of coupled oscillators, which he articulated circa 1967. Per the article, "the electronic states extend throughout the material in a periodic manner." That's a collective periodic oscillation. Then, "at low temperatures the magnetic moments assume the shape of a screw." That is also a collective periodic oscillation. (Winfree's usual phrase was "limit cycle oscillator.")

Art Winfree's coupled oscillator law is a general mathematical theory, which he applied more or less exclusively to biological synchronization. See Sync, the book by Steve Strogatz. But it also applies to multiferroics, Cooper pairs, and all other coherent behavior in physics, including phases of matter and their transitions. IMO.

Macksb
1 / 5 (1) Feb 23, 2013
The picture is a little busy, and thus hard to follow. One useful detail is the thin black line-four of them--which run from about 1 on the clock to about 7 on the clock. The black line is several inches long, placed there as a guide (though not called out in the text). Notice that the green arrow at the top of the thin black line is exactly antisynchronous to the partner at the bottom of the same line. This is an instance of coupled oscillators, following a standard, precise pattern in Winfree's model (0 and 180 degrees). Simple, but powerful.

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.