Magnetism generated by the geometric arrangement of Kagome star-shaped molecules

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The “kagome” star-shaped molecular structure of the 2D metal-organic material leads to strong electronic interactions and significant magnetic properties (left: STM image, right: non-contact AFM). Credit: FLEET

  • 2D kagome materials are a platform for tunable electron-electron interactions
  • “Star-like” atomic-scale kagome geometry “activates” magnetism in 2D organic material

A 2D nanomaterial made up of organic molecules bound to metal atoms in a specific geometry at the atomic scale exhibits significant electronic and magnetic properties due to strong interactions between its electrons.

A new study, published today, shows the emergence of magnetism in a 2D organic material due to strong electron-electron interactions; these interactions are the direct consequence of the unique, star-like structure at the atomic scale of the material.

This is the first observation of local magnetic moments emerging from interactions between electrons in an atomically thin 2D organic material.

The results have potential for applications in next-generation electronics based on organic nanomaterials, where tuning interactions between electrons can lead to a wide range of electronic and magnetic phases and properties.

Strong electron-electron interactions in a 2D organic body kagome Equipment

The Monash University study investigated a 2D metal-organic nanomaterial composed of organic molecules arranged in a kagome geometry, ie following a “star-shaped” model.

Dhaneesh kumar

“Where does local magnetism come from? Lead author Dr Dhaneesh Kumar asked and answered this key question. Local magnetism is the consequence of electron-electron interactions within the metal-organic 2D star assembly. Credit: FLEET

The 2D metal-organic nanomaterial consists of dicyanoanthracene (DCA) molecules coordinated with copper atoms on a low interacting metal surface (silver).

Using precise and atomically precise scanning probe microscopy (SPM) measurements, the researchers discovered that the 2D organometallic structure – whose molecular and atomic building blocks are in themselves non-magnetic – harbors confined magnetic moments. at specific locations.

Theoretical calculations have shown that this emerging magnetism is due to a strong Coulomb electron-electron repulsion given by the specific 2D kagome geometry.

“We believe this may be important for the development of future electronic and spintronics technologies based on organic materials, where tuning interactions between electrons can lead to control over a wide range of electronic and magnetic properties,” says FLEET CI A / Prof Agustin Schiffrin.

Direct survey of magnetism via the Kondo effect

Electrons in 2D materials with a kagome The crystal structure can be subjected to strong Coulomb interactions due to destructive interference of wave function and quantum localization, leading to a wide range of topological and strongly correlated electronic phases.

Such strong electronic correlations can manifest through the emergence of magnetism and, so far, have not been observed in atomically thin 2D organic materials. These can be beneficial for semiconductor technologies because of their ability to tune and self-assemble.

In this study, the magnetism resulting from strong Coulomb electron-electron interactions in a kagome organic matter was revealed through the observation of the Kondo effect.

“The Kondo effect is a multi-body phenomenon that occurs when magnetic moments are masked by a sea of ​​conduction electrons. For example, from an underlying metal, ”says Dr Dhaneesh Kumar, lead author and FLEET member. “And this effect can be detected by SPM techniques.”

“We observed the Kondo effect, and from there we concluded that the 2D organic material must harbor magnetic moments. The question then became “where does this magnetism come from?” “

Theoretical modeling by Bernard Field and his colleagues showed unambiguously that this magnetism is the direct consequence of strong Coulomb interactions between electrons. These interactions only appear when we bring the normally non-magnetic parts into a 2D kagome metallo-organic framework. These interactions hamper the pairing of electrons, with the spins of unpaired electrons giving rise to local magnetic moments.

“The theoretical modeling of this study offers a unique insight into the richness of the interaction between quantum correlations and topological and magnetic phases. The study gives us some clues on how these non-trivial phases can be controlled in 2D. kagome materials for potential applications in revolutionary electronic technologies, ”says FLEET CI A / Prof Nikhil Medhekar.

The study

Reference: “Manifestation of Strongly Correlated Electrons in a 2D Kagome Metal-Organic Framework” by Dhaneesh Kumar, Jack Hellerstedt, Bernard Field, Benjamin Lowe, Yuefeng Yin, Nikhil V. Medhekar and Agustin Schiffrin, September 12, 2021, Advanced functional materials.
DOI: 10.1002 / adfm.202106474

The research team consisted of FLEET experimenters and theorists from the School of Physics and Astronomy at Monash University and the Department of Materials Science and Engineering.

All the experiments were carried out at Monash University, with the support of the Australian Research Council (Center of Excellence and Future Fellowship programs). The numerical calculations performed at Monash were supported by resources provided by the National Computing Infrastructure (NCI) and the Pawsey Supercomputing Center. Further support was received from the Australian Government Research Training Program.

Scanning Probe Microscopy (SPM) at FLEET

A / Prof Schiffrin’s group at FLEET uses SPM to study atomic-scale properties – structural and electronic – of new nanomaterials with potential for future low-energy electronic technologies.

First Principles Theory Studies at FLEET

FLEET Assistant Professor Medhekar’s team uses first-principles atomistic modeling techniques to study the links between atomic-level structure and electronic properties of a wide range of nanomaterials, including low-dimensional materials that show promise for next-generation electronic technologies.

FLEET is a research center funded by the Australian Research Council and bringing together more than a hundred Australian and international experts to develop a new generation of ultra low power electronics.


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