International collaboration leads to new high-performance materials

Magnetoelectric materials, which convert magnetism to electricity and vice-versa, are promising for sensors, computer memory, wireless data transmission and charging, and biomedical tools, such as MRI scanners.

By combining techniques developed in labs halfway around the world from each other, researchers at Virginia Tech, the Korea Institute of Materials Science (KIMS), and the Korea Institute of Science and Technology (KIST) have developed a rapid method for manufacturing these materials that makes them unusually effective.

The research is led by Shashank Priya, the Robert E. Hord Jr. Professor of Mechanical Engineering in the College of Engineering at Virginia Tech and associate director for research and scholarship at the Institute for Critical Technology and Applied Science, and Jungho Ryu, principal researcher at KIMS.

Magnetic fields are readily available from the wires and appliances all around us: any device or wire that carries an electric current generates a magnetic field around itself. Priya and Ryu have designed a magnetic material that converts these ubiquitous magnetic fields into electricity.

The researchers' magnetoelectric material has two components: a magnetostrictive material that converts a magnetic field into deformation or vibration and a piezoelectric material that converts deformation or vibration into electricity.

When the two materials are sandwiched together and a magnetic field creates a mechanical deformation in the magnetostrictive material, it transmits that deformation to the piezoelectric material next door. Electricity is produced as a result.

The effect also works the opposite way, converting electricity to magnetism.

The effectiveness of the conversion process, called interface coupling, measures the degree to which a change in one material is transmitted to the other one.

“If all the strain that is generated could be transferred to the other side, that would be perfect coupling,” Priya said.

The better the contact between the two materials at the interface, the better the coupling.

At KIMS, Ryu had pioneered a technique for achieving exceptionally good contact between the two components by spraying granulated piezoelectric powders onto the magnetostrictive foil, allowing direct coating of one material onto another.

“Just like air-brushing paint on a car, you’re spraying a coating of this solid powder, layer by layer. The powder is crystalline and has microscale dimensions, so the adhesion on impact is quite strong,” Ryu explained.

With this composite material in hand, the team used a laser-annealing technique developed in Priya’s lab to boost its performance.

Shining a laser onto the layered material gives the glass-like piezoelectric film a more crystalline structure that converts strain to electricity more effectively.

This structural change is most dramatic on the surface, and decreases deeper in the material where the laser doesn’t penetrate as strongly. At the interface between the two sides, the piezoelectric powder remains glassy, preserving the smooth contact.   

When the researchers tested the material created using this method, the magnetoelectric coupling was two orders of magnitude higher than values for other similar materials; in fact, it was almost at its theoretical maximum.

“They are the leaders in this powder-deposition technique, and we have had this laser-annealing research going on for the last few years. We combined our strengths to get this result,” Priya said.

Priya has been collaborating with researchers from KIMS for more than 10 years; during this project, Ryu spent four months working at Virginia Tech.

Hosting visiting scientists is common for Priya, who explains that visitors often inspire entirely new research directions by bringing unique techniques from their own labs and ideas about how they could be combined with the host’s work.

“It cuts down our learning curve, because you are starting with the best scientists,” Priya said. “You can accomplish a lot in a very short time.”

The project was funded in part by the U.S. Office of Naval Research and its global office located in Tokyo, which helps build international research collaborations. Magnetoelectric materials could be used in self-powered sensor nodes to detect mechanical or electrical failures on naval vessels.