Atomic-scale Control of Graphene Magnetism by Using Hydrogen Atoms

Condensed Matter Physics Centre at the Universidad Autónoma de Madrid (IFIMAC-UAM)
  • IFIMAC and CIC nanoGUNE collaborated in the elusive experimental realisation of theoretical predictions of inducibility of magnetism in graphene
  • Successful induction of magnetism in graphene by means of chemiadsorption of hydrogen atoms
  • Results open way for fine-tuning of graphene magnetism and breakthroughs in computation and data storage

 

Graphene, its properties and promises

Graphene is still a relatively recent material, being isolated for the first time back in the year 2004. It displays many extraordinary physicochemical properties, including a very high conductivity, extreme mechanical strength, or a rather large white light absorption capacity (particularly, considering its one-atom thickness).

The incorporation of magnetism to the list of graphene properties has long been pursued. Nonetheless, despite its particular electronic characteristics, magnetism kept for years eluding the list of properties experimentally proven for graphene. Despite this, since the early days of graphene research theoretical predictions agreed that graphene could be magnetized at will by the adsorption of single hydrogen atoms. The realisation of such an adsorption phenomenon (a type of reversible adhesion of a molecule to a surface) in the necessary way remained elusive.

 

Graphene and hydrogen: a magnetic team

The efforts to reproduce the predictions experimentally had been unsuccessful, mainly due to the difficulties of providing at the same time an atomistic characterization (the precise “mapping” of the atoms present), together with the fine control of the hydrogenated graphene samples.

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STM topography of single H atom chemisorbed on graphene. Lines illustrate the magnetic field induced by the H atom in graphene.

Research from an international team including the SOMMa members IFIMAC Condensed Matter Physics Center, and CIC NanoGune overcame this challenge, even going beyond theoretical expectations. Other participants encompassed the Department of Condensed Matter Physics and Nicolás Cabrera Institute of the Autonomous University of Madrid; the Neél Institute of the University of Grenoble – Alpes / Centre National de la Recherche Scientifique (France); and the Department of Physics of the Faculty of Science of the Zagazig University (Egypt).

The work showed how the absorption of single H atoms on graphene sheets magnetizes the graphene regions around them. In contrast to common magnetic materials, where the magnetic moment (or “magnetic force”) is localized in the small space of a few angstroms, the induced graphene magnetic moments on graphene sheets extends over several nanometers of its surface. In addition, it becomes possible to present an atomically modulated spin texture, in practice providing the means to better control the “shape” of the magnetic field generated.

Results proved that the induced magnetic moments couple strongly (i.e. add or neutralize each other) at very long distances, following a particular rule: magnetic moments were found to sum-up or neutralize one another depending on the relative H-H adsorption sites; that is, depending on the position of the involved atoms. Equally importantly, the controlled manipulation of single H atoms was achieved.

The unexpected possibility to arrange H atoms on graphene with any desired geometry will enable to do experiments restricted so far to a pure theoretical framework. The implications of these results entail that it is possible to tune selectively the collective magnetic properties of specific graphene regions.

Results of this development, explained in 3 minutes.

For example, the magnetization of selected graphene areas allows for injection in-situ of so-called “spin currents”. Such “spin currents” can be understood as “streams” of magnetic state change inside a material, as if a switch could turn on or off the magnetism exhibited by (parts of) that material. This, unlike happens in electromagnetism, would happen without the intervention of electric current. The results and their meaning are summarized in the video shown next.

The possibilities opened by selective magnetization of graphene also avoid the use of ferromagnetic electrodes and the problems associated with ferromagnet-graphene contacts (as for instance, “parasite” currents). Likewise, possibilities are opened for creating “spin valves” and magnetoresistive devices made of carbon, which anticipates unlimited uses of graphene in the discipline of spintronics, with enormous connotations in fields as those of information storage or quantum computing, among others.

 

Image/video credits:

The image and video displayed were kindly provided by IFIMAC.

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