Non-Magnetic Materials Reveal new Secrets About Their Structure

Non-magnetic materials, such as those routinely used in the manufacturing of computer components, have been exposed recently by researchers from the Pennsylvania State University as to having electrical and mechanical properties that could potentially make their applications much broader than they currently are. Similarly to other types of materials, the properties of non-magnetic materials are determined by their internal 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," explains Venkatraman Gopalan of Penn State's Center of Nanoscale Science, leader of the new study.

Previous information regarding non-magnetic material suggested that they have 32 different crystal symmetries, while magnetic materials are known to have 90 different point group symmetries, which can be accounted through the fact that the atoms have magnetic spins. "Motion is an extremely important aspect of magnetism. Magnetism develops in nature as soon as charged particles start moving or spinning," said Gopalan.

The higher number of point group symmetries was believed to give magnetic materials more properties than those of non-magnetic materials, since the spin of an atom can flip, thus adding yet another symmetry, however the new study reveals that non-magnetic materials should in fact have a number of symmetries identical to those of magnetic materials. Theoretically, this is accomplished inside the material as groups of atoms are distorted through twisting or rotation. By doing so, the material gains properties that were once thought to belong only to magnetic materials.

In the experiment, a non-magnetic material known as strontium titanate cooled to a low enough temperature responded by twisting the oxygen atoms into a tighter position in order to save energy. "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," said Gopalan.

A further study of the twisting movement predicted that the optical properties of non-magnetic materials known as roto second harmonic generation is similar to the magnetic second harmonic generation, which is usually characteristic to crystals emitting laser radiation, that use it to convert infrared radiation to green light. Indeed, titanate material was later found to posses a small 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.

"These materials are used in hundreds of applications, but this new work holds great promise for finding many more uses," said Peter Schiffer, associate vice president for research and a professor of physics at Penn State.