Researchers at Boston College and the University of California, Santa Barbara have discovered a significant rearrangement of magnetic domains through thermal cycling in Mott insulators

Image: This image shows iridium oxide bulk single crystal Sr3Ir2O7, in which the researchers introduced lanthanum as a partial substitute for strontium (Sr) to bring the system close to antiferromagnetic transition. A team from Boston College and the University of California, Santa Barbara recently reported in the journal Science Advances on the atomic-scale visualization of the temperature-driven magnetic pattern spatial variation in Mott insulators. see more 

Chestnut Hill, Massachusetts (11/16/2021)-The team reported in "Science Advances" that an experiment led by a team of researchers at Boston College made the temperature-driven magnetic mode in Mott’s insulators spatially variable atomic scales Visualization becomes possible.

Ilija Zeljkovic, associate professor of physics at Boston College, said that today's cutting-edge materials are usually "bulky" on the nanoscale: their electronic and magnetic properties vary to a few nanometers on the length scale.

Zeljkovic started the project with Wang Ziqiang, a professor of physics at Boston College, and Zhao He, a recent doctoral student. , And a collaborator at the University of California, Santa Barbara.

Zeljkovic added that a particularly interesting transition involves a non-magnetic material that becomes magnetic. This transformation can be achieved by cooling the material to a low temperature or by adjusting its elemental composition. Although significant progress has been made in the overall understanding of magnetic materials, little is known about the atomic-level properties of magnetic transitions.

The researchers wrote in an article entitled "Imaging the fluctuations and effects of atomic-scale disorder in antiferromagnetic domain doped spin-orbit Mott insulators."

Zeljkovic said that antiferromagnetism is an unusual magnetism in materials, which occurs when the electron spins of adjacent atoms are aligned in opposite directions. The team reports that it uses a spin-polarized scanning tunneling microscope (SP-STM) to map the local intensity of antiferromagnetic ordering on nanometer length scales.

The researchers discovered a significant rearrangement of magnetic domains through thermal cycling.

"For example, some magnetic areas of the sample will become non-magnetic, and vice versa, some areas that were once non-magnetic will become magnetically ordered after thermal cycling," Zeljkovic said. "We also found that magnetic domains locally'avoid' lanthanum substitution and tend to form away from these impurities."

Zeljkovic said that the team used a statistical analysis method called cluster analysis theory to analyze the size and distribution of domains, which can provide insight into whether domains are completely randomly distributed.

"We found that the domains are not randomly distributed, which means that electronic correlations or electron-electron interactions may play an important role in the emergence of domains," Zeljkovic said.

This work builds on previous research, in which Zeljkovic and colleagues visualized antiferromagnetic patches or magnetic domains in the related doped Mott insulator Sr2IrO4.

"We want to study what determines the size and spatial distribution of these domains in Sr3Ir2O7," Zeljkovic said. "In addition, we began to explore whether and how the magnetic domains change if the material is heated to become non-magnetic and then cooled back to its magnetically ordered state."

Based on the latest findings, Zeljkovic said that the next step in research will seek to extend this technology to other complex oxides and materials with different types of magnetic states (such as ferromagnetism).

Influence of Atomic-scale Disorder in Imaging Antiferromagnetic Domain Fluctuations and Doped Spin-Orbit Mott Insulators

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Ed Hayward Boston College ed.hayward@bc.edu Office: 617-552-4826

Ilija Zeljkovic Boston College ilija.zeljkovic@bc.edu

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Copyright © 2021 American Association for the Advancement of Science (AAAS)