Magnetism or no magnetism? The influence of substrates on electronic interactions

Magnetism or no magnetism? The influence of substrates on electronic interactions
Schematic depiction of interaction-induced magnetism in a 2D MOF and how substrates influence it. a Ball-and-stick models of DCA and Cu, the components of the MOF, and their isolated electronic structures. The copper(I) ions and DCA molecules in the MOF are not intrinsically magnetic. b Ball-and-stick model of DCA-Cu kagome MOF, where intra-MOF electron-electron Coulomb interactions induce magnetic moments. The MOF has a kagome electronic band structure derived from the DCA LUMO (non-spin-polarized schematic shown). c Ball-and-stick model of DCA-Cu MOF on a substrate and schematic band structures. The magnetism in the MOF is influenced by coupling to the substrate, charge transfer either out of or into the MOF (such as by an applied electric field), and strain, which alters the bandwidth. The strength of the magnetic moments can be enhanced by using a weakly interacting substrate, favorable electron filling of the MOF by choice of substrate work function or application of electric fields, and by applying tensile strain to the MOF such as by lattice mismatch. (HOMO: highest occupied molecular orbital. LUMO: lowest unoccupied molecular orbital). Credit: npj Computational Materials (2022). DOI: 10.1038/s41524-022-00918-0

A new study at Monash University illustrates how substrates affect strong electronic interactions in two-dimensional metal-organic frameworks.

Materials with strong electronic interactions can have applications in energy-efficient electronics. When these materials are placed on a , their are changed by charge transfer, strain, and hybridization.

The study also shows that electric fields and applied strain could be used to "switch" interacting phases such as on and off, allowing potential applications in future energy-efficient electronics.

Turning magnetism on and off with substrates

Strong interactions between electrons in materials gives rise to effects such as magnetism and superconductivity. These effects have uses in magnetic memory, spintronics, and quantum computing, making them appealing for emerging technologies.

Last year, another study at Monash discovered strong electronic interactions in a 2D . The researchers found signatures of magnetism in this material. They showed that this magnetism arose due to strong interactions that were only present when the non-magnetic components were brought together.

This material was grown on a metallic substrate. The substrate was important for the growth and measurement of the material.

"We observed this effect when the material was grown on silver, but not when it was grown on copper, despite them being very similar," says Bernard Field (Monash), co-author of the earlier study and lead author of the current study.

"So that begged the question: Why did the material behave so differently on different substrates?"

The researchers simulated the metal-organic framework on many different substrates to determine under what conditions magnetism could emerge.

They also created a simple model which accurately described the physical phenomena in their atomic-scale simulations. This model allowed the team to quickly and easily explore a wider range of systems with fine control over the important parameters.

Three key variables were found to determine the effect of substrates on electronic interactions: charge transfer, strain, and substrate hybridization.

  • Charge transfer is when a substrate gives or takes electrons from the 2D material. The effect of interactions was strongest when the material had one free electron per molecule.
  • Strain is when a substrate stretches or squeezes the 2D material. When the material is stretched, electrons have difficulty moving between molecules and atoms, so they experience local interactions more strongly.
  • Hybridization is when the electronic character of the substrate and the 2D material are mixed due to coupling between them. Metallic substrates often have strong hybridization, which can suppress magnetism. But insulating substrates, such as atomically-thin hexagonal boron nitride, have very weak hybridization and preserve the electronic interactions in the material.

With this understanding of what the key variables are, it is possible to consider how to manipulate these variables to control the electronic interactions.

The study showed that an could turn magnetism on and off by changing the charge transfer.

Electric fields are how existing transistors operate. Having electric control of magnetic phases is vital for using these materials in .

The study also showed that applied strain could turn magnetism on and off. This could be achieved using piezoelectric materials. It is also an important consideration for flexible electronics.

"The team is continuing to investigate strong interactions in 2D metal-organic frameworks, which provide a rich platform to explore novel quantum physics applied for energy-efficient electronic devices," says corresponding author Prof Nikhil Medhekar (Monash Department of Materials Science and Engineering), who led the study, "We are investigating more advanced methods for simulating between electrons."

"This work provides quantitative predictions, using diverse theoretical formalisms, on the electronic properties of low-dimensional nanomaterials on a wide range of substrates and conditions," says co-author A/Prof Agustin Schiffrin (Monash School of Physics and Astronomy), who leads on these materials, "This can guide future real-world experiments, which is extremely valuable for experimental researchers."

"Correlation-induced magnetism in substrate-supported 2D " was published in npj Computational Materials in November 2022.

More information: Bernard Field et al, Correlation-induced magnetism in substrate-supported 2D metal-organic frameworks, npj Computational Materials (2022). DOI: 10.1038/s41524-022-00918-0

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Citation: Magnetism or no magnetism? The influence of substrates on electronic interactions (2022, November 9) retrieved 27 November 2022 from https://phys.org/news/2022-11-magnetism-substrates-electronic-interactions.html
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