Magnetism generated in a 2D organic material by an arrangement of star-shaped molecules


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

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 a direct consequence of the material’s unique star-shaped atomic-scale structure.

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 kagome material

The Monash University study investigated a 2D metal-organic nanomaterial made up of organic molecules arranged in a kagome geometry, that is, in a “star-shaped” pattern.

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 magnetic moments. confined to 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 electronics and spintronics technologies based on organic materials, where tuning interactions between electrons can lead to the control of a wide range of electronic and magnetic properties,” says FLEET CI A / Prof Agustin Schiffrin.

Magnetism generated in a 2D organic material by an arrangement of star-shaped molecules

Confirmation of the Kondo effect, via electron state density tunneling spectroscopy measurements, confirms the presence of local magnetism in the 2D metal-organic framework. Credit: FLEET

Direct survey of magnetism via the Kondo effect

Electrons in 2D materials with a kagome 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 2D kagome organic material 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 lead author and member. of FLEET, Dr Dhaneesh Kumar. “And this effect can be detected by SPM techniques.”

“We observed the Kondo effect, and from there we concluded that the organic 2D 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 introduce the normally non-magnetic parts into a 2D kagome metal-organic frame. 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 provides us with some clues as to how these non-trivial phases can be controlled in materials. 2D kagome for potential applications in revolutionary electronic technologies, ”says Prof. FLEET CI A / Prof Nikhil Medhekar.

Kagome graphene promises exciting properties

More information:
Dhaneesh Kumar et al, Manifestation of strongly correlated electrons in a 2D Kagome metal-organic framework, Advanced functional materials (2021). DOI: 10.1002 / adfm.202106474

Quote: Magnetism generated in a 2D organic material by an arrangement of star-shaped molecules (2021, September 13) retrieved October 26, 2021 from star-like-molecules .html

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