- The magnetic state of a small triangular structure of graphene, with only 40 carbon atoms, has been detected
- This finding is the result of a collaboration between experimental and theoretical scientists at CiQUS, which belongs to the Universidade de Santiago de Compostela, Donostia International Physics Center (DIPC) and CIC nanoGUNE
- This work expands the field of applications of this prodigious material in areas such as ICT
Researchers at CiQUS, from the Universidade de Santiago de Compostela (USC), coordinated by Diego Peña, from Donostia International Physics Center (DIPC) and CIC nanoGUNE, are making progress in deciphering the magnetism of a small triangular piece of graphene, thus expanding the knowledge on this versatile material and its potential applications in different fields of everyday life. It is the first experimental evidence, after using a tunneling microscope (which captures images of surfaces at the atomic level), of the inherent magnetism of a small triangular structure of graphene.
Graphene, a magnet for multiple sectors
Graphene is a diamagnetic material, which means that it is repelled by magnetic fields and is reluctant to magnetize. Despite this, however, some theoretical calculations predict that a triangular structure of this material could become magnetic. This apparent contradiction arises from the fact that, for certain “magic” shapes of graphene, electrons seem to “rotate” more easily in a certain direction, to put it rather colloquially, which means that they have the same spin and, thus, make it become magnetic. Triangulene is a triangular structure of graphene where, as predictions asserted, a pure magnetic state can be achieved. In other words, it is like a magnet of nanometric dimensions. Giving magnetism to graphene opens up fascinating prospects for its application in, for example, quantum technologies.
However, despite strong and clear predictions about triangulene magnetism, there was, to date, no clear experimental evidence on this. On the one hand, production of triangulene by organic synthesis methods is a very difficult solution because the biradical character of this molecule makes it very reactive. Furthermore, its magnetism seems to be extremely elusive in those few successful cases.
Now, this new Basque-Galician study, published in Physical Review Letters [1] scientific journal, has resumed this challenge by using a tunneling microscope (STM). After producing with atomic precision a triangular piece of graphene of a couple of nanometers in size on a clean gold surface, tunneling spectroscopy measurements revealed that this compound has a net magnetic state characterised by a S=1 spin and, therefore, that this molecule is a small, pure carbon “paramagnet”. These results constitute the first experimental evidence of a high-spin graphene structure.
One step further
These findings have been complemented by an experiment consisting of the atomic manipulation of triangulene by-products: some structures were formed with more hydrogen atoms than they should be, and these atoms passivated their magnetism. By controlled one-by-one extraction of these hydrogen atoms with a STM, researchers observed how triangulene magnetism was recovering step by step.
The experimental evidence of triangulene magnetism faced an additional difficulty. As opposed to the macroscopic magnet, the “paramagnet” does not have well-defined poles due to its small size. For this reason, its magnetic state could not be detected with more conventional spectroscopy techniques, where the orientation of the magnet’s magnetism could facilitate its detection. In this work, experimental evidence of its magnetic state was obtained through the detection of the multichannel Kondo effect – an “exotic” version of the traditional Kondo effect described in the 1960s – which can arise in complex magnetic systems. Its observation in a graphene triangular structure of only 40 carbon atoms is a milestone which can open up a new horizon in our understanding of the origin of this magnetism and of its possible integration in more complex magnetic structures.
This work has been carried out within the framework of SPRING FET Open, Spin Research in Graphene, a European project led by Jose Ignacio Pascual, Ikerbasque researcher at nanoGUNE. The long-term objective of this project is the development of an environmentally friendly all-graphene platform where spins can be used for carrying, storing and processing information.
Bibliographic reference:
Uncovering the Triplet Ground State of Triangular Graphene Nanoflakes Engineered with Atomic Precision on a Metal Surface
Jingcheng Li, Sofia Sanz, Jesus Castro-Esteban, Manuel Vilas-Varela, Niklas Friedrich, Thomas Frederiksen, Diego Peña and Jose Ignacio Pascual
Phys. Rev. Lett. 124, 177201 – Published 27 April 2020
https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.124.177201
