Atomic-scale control of graphene magnetism using hydrogen atoms
Final Report Abstract
The main goal of this project was to demonstrate experimentally that 2D materials, in particular graphene, can be magnetized at will by adsorption of individual hydrogen atoms. This possibility was demonstrated in the project by experiments performed by our project partner Prof. Ivan Brihuega and his team. They showed that the adsorption of a single H atom on a decoupled graphene layer induces a spin-polarized state. We were able to confirm his results at even lower temperatures and, by applying an external magnetic field, showed that these states split at sufficiently high field strengths, confirming the magnetic nature of the state observed after H atom adsorption. We then went on to study the influence of hydrogen adsorption on a complementary 2D material, the so-called "white graphene", h-BN, which is not a semimetal like graphene, but a wide bandgap insulator. Here, we showed that the number of hydrogen atoms bound to single Co-atoms allows tuning their spin state from S = 1/2 to S = 1 and S = 3/2. Furthermore, we showed that the coupling of these spin systems in controlled matter to a Co-functionalized tip allows to characterize the nature of the coupling of the spin systems to their corresponding electronic bathes. Since the number of hydrogen atoms determines the spin state of the CoH complexes on h-BN, we functionalized the probe tip with hydrogen and coupled it to a magnetic S = 1 CoH complex. Here we observed the transition of the magnetic moment from S = 1 to S = 1/2 accompanied by a drastic change of the spectroscopic feature. The flat spectrum with spin excitations at symmetric energies around the Fermi level changes to a strong peak at zero energy due to the Kondo screening of the doubly degenerate S = 1/2 states. We studied this transition in detail with atomic force spectroscopy, which visualized the phase transition as a kink in the potential energy landscape.
Publications
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Quantum engineering of spin and anisotropy in magnetic molecular junctions. Nature Communications, 6(1).
Jacobson, Peter; Herden, Tobias; Muenks, Matthias; Laskin, Gennadii; Brovko, Oleg; Stepanyuk, Valeri; Ternes, Markus & Kern, Klaus
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Correlation-driven transport asymmetries through coupled spins in a tunnel junction. Nature Communications, 8(1).
Muenks, Matthias; Jacobson, Peter; Ternes, Markus & Kern, Klaus
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Potential energy–driven spin manipulation via a controllable hydrogen ligand. Science Advances, 3(4).
Jacobson, Peter; Muenks, Matthias; Laskin, Gennadii; Brovko, Oleg; Stepanyuk, Valeri; Ternes, Markus & Kern, Klaus
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Local stiffness and work function variations of hexagonal boron nitride on Cu(111). Beilstein Journal of Nanotechnology, 12, 559-565.
Grewal, Abhishek; Wang, Yuqi; Münks, Matthias; Kern, Klaus & Ternes, Markus
