Indian-origin researcher unveils new properties of non-magnetic materials

Washington, June 12 : Led by an Indian-origin researcher, a team of Penn State experts has identified several new properties of non-magnetic materials.

Venkatraman Gopalan, a professor of materials science and engineering, says that the findings suggest that the entire class of non-magnetic materials, such as those used in some computer components, could have considerably more uses than scientists had thought.

He says that the findings attain significance as they reveal previously unknown information about the structure of such materials, expanding the number of properties that they potentially could have.

Describing the research team's work in a research paper, scheduled for publication in the journal Physical Review Letters, Gopalan said that a material's properties are determined by its structure.

"If I was out hiking and I found a rock that contained a quartz crystal, I could tell you what properties the crystal can and cannot have just based on what we call its symmetry--the number and arrangement of crystal planes it has. Symmetry results from the way the atoms are arranged in the quartz. It is an extremely powerful way of understanding our world," he said.

Gopalan says that the non-magnetic materials his team studied were thought to have one of the 32 different crystal symmetries-called point group symmetries-known to exist in nature.

He also says that magnetic materials, on the other hand, have 90 different point group symmetries because their atomic particles have magnetic spins, which can be imagined as tiny loops of current.

"Motion is an extremely important aspect of magnetism. Magnetism develops in nature as soon as charged particles start moving or spinning," said Gopalan.

He points out that scientists have to date thought that symmetry enables magnetic materials to have more properties than non-magnetic materials because flipping the direction of spin creates an additional symmetry.

However, his team's new theory suggests that non-magnetic materials can have just as many properties as magnetic materials.

Gopalan says that some non-magnetic materials have groups of atoms that distort by twisting or rotating.

He likens this slight movement to a tiny loop of current, and says that it is enough to give the material some additional properties that previously were thought to belong only to magnetic materials.

When he and his colleagues tested their theory experimentally using a non-magnetic material called strontium titanate, they found that its oxygen atoms responded by twisting into a tighter position to save energy and space upon the cooling of the material.

"The oxygen atoms don't rotate all the way around like a loop of current does in magnetic materials, but theoretical analyses show that they do twist and, therefore, it is possible that these materials could have previously unknown properties," he said.

Gopalan and his colleagues later tested whether the twisting movement translated into the expression of additional properties.

The researchers, in particular, predicted and tested for an optical property that they call roto second harmonic generation, which is analogous to a well-known property called magnetic second harmonic generation.

Second harmonic generation is found in the crystals that are used in green laser pointers to convert infrared laser light into green laser light.

The study revealed that the strontium titanate material does have a small amount of roto second harmonic generation.

"Nobody has thought of relating magnetic symmetries to a non-magnetic material like strontium titanate, but that's precisely what our paper does. We first did a theoretical analysis in which we applied the symmetry framework that traditionally is used to describe magnetic materials to this vast class of non-magnetic materials.

Then we did a laboratory experiment with a particular non-magnetic material and we found that it has a property that previously was thought to belong only to magnetic materials. We suggest that it is possible for the entire class of non-magnetic materials to have more symmetries and more properties than previously have been thought possible," said Gopalan.

Peter Schiffer, associate vice president for research and a professor of physics at Penn State, believes that the new findings may lead to an explosion of research into new properties of non-magnetic materials and to possible applications of these properties.

"These materials are used in hundreds of applications, but this new work holds great promise for finding many more uses," he said.

Gopalan's team is planning to investigate additional non-magnetic materials, with an ultimate goal of producing a new catalog of materials and their properties.

ANI