Professors Hereman and Trivedi Author Groundbreaking Study

Researchers have discovered a new electronic property at the frontier between the thermal and quantum sciences in a specially engineered metal alloy – and in the process identified a promising material for future devices that could turn heat on and off with the application of a magnetic “switch.”

“Solid-state heat switches without moving parts are extremely desirable, but they don’t exist,” Heremans said. “This is one of the possible mechanisms that would lead to one.”

In physics, an anomaly – the electrons’ generation and absorption of heat discovered in this study – refers to certain symmetries that are present in the classical world but are broken in the quantum world, said study co-author Nandini Trivedi, professor of physics at Ohio State.

The research was published June 7, 2021 in the journal Nature Materials.

Read more here.

Tiny magnetic particles enable new material to bend, twist and grab

A CEM-supported research team from The Ohio State University and the Georgia Institute of Technology has developed a material system that can transform into different shapes through the application of magnetic fields.

The new material, called magnetic shape memory polymers, has the potential to enable a wide range of applications, from biomedical devices to soft robotics. The novel magnetic shape memory polymer composite enables tunable rigidity and has multiple shape manipulation capabilities.

The discovery was reported in the most recent issue of Advanced Materials.

“The new functional soft material enables the development of new advanced material systems that could potentially revolutionize multifunctional robots and machines,” said Renee Zhao, an assistant professor in Mechanical and Aerospace Engineering (MAE). Zhao served as co-principal investigator with H. Jerry Qi, professor of Mechanical Engineering at Georgia Tech.

The new materials integrates fast reversible and reprogrammable actuation, shape locking, and untethered operation for applications in soft robotics, actuators with large gripping force, morphing structures, deformable electronics, especially for designing active and adaptive guidewires, catheters, and stents that could potentially enable the next generation of biomedical devices for minimally invasive operations.

The material is novel in that it achieves multiple shape manipulations in a single material system.

“One of the big challenges in the soft active materials field is how to integrate various shape manipulations into one material system for multifunctional purposes, as many such manipulations are contradictory to each other,” Zhao said. “For example, fast reversible shape change requires that the material can respond to external stimulus rapidly, but shape locking needs the material to have no response or needs to maintain the external stimulus, which requires a constant energy input.”

The magnetic shape memory polymer composite is comprised of an amorphous shape memory polymer matrix of two types of magnetic particles. Researchers were able to soften the matrix and make it pliable by applying a high-frequency, oscillating magnetic field to heat the iron oxide particles and raise the temperature of the actuated shape. Applying a second magnetic field caused rapid and reversible shape change under actuation magnetic fields. Once the shape memory polymers cooled, the shape locked in position.

In a locked state, the strength of the material allowed an actuated gripper to lift up to 1,000 times its own weight. On top of this, the material is adaptive to extreme conditions, allowing application for an array of uses, Zhao said.

“The degree of freedom is limited in conventional robotics,” she said. “With soft materials, that degree of freedom is unlimited.”

Other Ohio State investigators included MAE postdoc Qiji Ze, MAE students Shuai Wu and Rundong Zhang, as well as CEM faculty member Fengyuan Yang, professor of Physics and director of the Center for Exploration of Novel Complex Materials.

The research was supported by Ohio State’s Materials Research Seed Grant Program, funded by the Center for Emergent Materials, an NSF-MRSEC; the Center for Exploration of Novel Complex Materials; and the Institute for Materials Research. Research was also supported by the National Science Foundation (NSF), with an award to Ohio State through NSF’s Materials Research Science and Engineering Centers.

Cross-IRG Research Published in Physical Review Letters

This week, CEM members from all three IRG’s had a joint paper published in Physical Review Letters‘ first issue of 2020. The paper, titled “Fundamental Spin Interactions Underlying the Magnetic Anisotropy in the Kitaev Ferromagnet CrI3“, was co-authored by IRG-1 co-lead Prof. Nandini Trivedi, IRG-2 co-lead Prof. Joshua Goldberger, and Director and IRG-3 member Prof. Chris Hammel, as well as several CEM grad students. Funded primarily by CEM, the researchers also collaborated with scientists at the National High Magnetic Field Laboratory and the Korea Institute for Advanced Study. The paper can be read on the Physical Review Letters website

CEM Facilities Utilized for Research Published in Science Advances

Last week, IRG-2 member Jeanie Lau’s paper “Correlated insulating and superconducting states in twisted bilayer graphene below the magic angle” was published in Science Advances.

Lau, professor of physics at Ohio State and lead author on the paper, and her team studied the “magic angle” that makes graphene layers become a superconductor, meaning they are able to conduct electricity without resistance, suffering no loss of energy. The team found that graphene layers remained supconductive over a smaller angle than previously thought possible, opening up more possibilities for their use in real world applications.

The NanoSystems Laboratory, a CEM-supported research facility at Ohio State, was utilized for device fabrication necessary to perform experiments for this study.

Lau and other Ohio State researchers collaborated with scientists at the University of Texas- Dallas and the National Institute for Materials Science in Japan. More information about this research and the team can be found on Ohio State’s news website. You can read the paper on the Science Advances website.


CEM IRG-3 Faculty Member Published in Science Advances

Jos Heremans, Ohio State professor of mechanical and aerospace engineering and CEM IRG-3 co-lead, along with an international team of researchers from North Carolina State University, Oak Ridge National Laboratory, and the Chinese Academy of Sciences, recently published the paper “Paramagnon drag in high thermoelectric figure of merit Li-doped MnTe” in Science Advances.

The researchers found that local thermal perturbations of spins in a solid can convert heat to energy even in a paramagnetic material- where spins weren’t thought to correlate long enough to do so. This effect, which the researchers call “paramagnon drag thermopower,” converts a temperature difference into an electrical voltage. This discovery could lead to more efficient thermal energy harvesting.

“Before this work, it was believed that magnon drag could exist only in magnetically ordered materials, not in paramagnets,” said Prof. Heremans. “Because the best thermoelectric materials are semiconductors, and because we know of no ferromagnetic semiconductor at room temperature or above, we never thought before that magnon drag could boost the thermoelectric efficiency in practical applications. This new finding changes that completely; we can now investigate paramagnetic semiconductors, of which there are a lot.”

This research was supported in part by CEM. More information about this research and the team can be found in the press release from North Carolina State University. You can read the paper on the Science Advances website.