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Experiments visualize temperature-related spat | EurêkAlert!

image: This image shows a loose single crystal of iridium oxide, Sr3Ir2O7, in which the researchers introduced lanthanum as a partial substitute for strontium (Sr) in order to bring the system closer to the antiferromagnetic transition. The team at Boston College and UC Santa Barbara have revealed atomic-scale visualization of a spatial change in temperature-induced magnetic patterns in a Mott insulator, they recently reported in Science Advances.
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Credit: Boston College

Chestnut Hill, Mass. (11/16/2021) – Experiments by a group of researchers at Boston College have visualized at the atomic scale of a spatial change in temperature-induced magnetic patterns in a Mott insulator, the team reported in Scientists progress.

Today’s advanced materials are often ‘lumpy’ at the nanoscale: their electronic and magnetic properties vary over length scales down to a few nanometers, said Boston College associate professor of physics Ilija Zeljkovic.

This “inhomogeneity” can be particularly pronounced near a phase transition, where the material changes, or passes, into a different phase from the material, said Zeljkovic, who led the project with the Boston College physics professor. Ziqiang Wang, recent Ph.D. He Zhao. , and collaborators from the University of California, Santa Barbara.

One particularly intriguing transition involves a non-magnetic material that becomes magnetic, Zeljkovic added. This transition can be achieved by cooling the material to low temperature, or by adjusting its elemental composition. Although significant advances have been made in the understanding of magnetic materials as a whole, very little is known about the atomic-scale nature of magnetic transitions.

The researchers studied an iridium oxide single crystal, Sr3Ir2O7, in which they introduced lanthanum as a partial substitute for strontium (Sr) in order to bring the system closer to the antiferromagnetic transition, the team reported in an article titled ” Imaging antiferromagnetic domain fluctuations and the effect of atomic-scale disorder in a spin-orbit-doped Mott insulator.

Antiferromagnetism is an unusual type of magnetism in a material, Zeljkovic said, which occurs when the spins of electrons at nearby atomic sites are aligned in exactly opposite directions. The team reports using spin polarization tunneling microscopy (SP-STM) to map the local strength of the antiferromagnetic order at nanometer-length scales.

Researchers have discovered a dramatic rearrangement of magnetic domains with thermal cycling.

“For example, some regions of the sample that were magnetic would become non-magnetic, and vice versa, some areas that were previously non-magnetic would become magnetically ordered after a thermal cycle,” Zeljkovic said. “We also found that magnetic domains locally ‘avoid’ lanthanum substitutions and tend to form from these impurities. “

The team used a statistical analysis method called Cluster Analysis Theory to analyze the size and distribution of domains, which can tell whether or not domains are completely randomly distributed, Zeljkovic said. .

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

The work built on previous research, where Zeljkovic and his colleagues visualized antiferromagnetic patches, or domains, in a related doped Mott insulator, Sr2IrO4.

“We wanted to study what defines the size and spatial distribution of these domains in Sr3Ir2O7,” Zeljkovic said. “In addition, we set out to explore if and how the domains will change if the material is reheated to become non-magnetic and cooled to its magnetically ordered state.”

Based on the most recent findings, Zeljkovic said that the next steps in the research will aim to extend this technique to other complex oxides, as well as materials with different types of magnetic states, such as ferromagnetism.


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