Graphene Spintronic Devices with Molecular Nanomagnets (original) (raw)
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Graphene as a Reversible Spin Manipulator of Molecular Magnets
Physical Review Letters, 2011
One of the primary objectives in molecular nano-spintronics is to manipulate the spin states of organic molecules with a d-electron center, by suitable external means. In this letter, we demonstrate by first principles density functional calculations, as well as second order perturbation thoery, that a strain induced change of the spin state, from S=1 → S=2, takes place for an iron porphyrin (FeP) molecule deposited at a divacancy site in a graphene lattice. The process is reversible in a sense that the application of tensile or compressive strains in the graphene lattice can stabilize FeP in different spin states, each with a unique saturation moment and easy axis orientation. The effect is brought about by a change in Fe-N bond length in FeP, which influences the molecular level diagram as well as the interaction between the C atoms of the graphene layer and the molecular orbitals of FeP.
Addressing a Single Molecular Spin with Graphene-Based Nanoarchitectures
Molecular Architectonics, 2017
Finding reliable methods to exploit molecular degrees of freedom represents an intriguing problem involving the control of new mechanisms at the nanoscale and several technological challenges. Here, we report a novel approach to address a single molecular spin embedded in an electronic circuit. Our devices make use of molecules with well-defined magnetic anisotropy (TbPc 2) embedded in nanogapped electrodes obtained by electroburning graphene layers. Such devices work as molecular spin transistors allowing the detection of the Tb spin flip during the sweep of an external magnetic field. The spin readout is made by the molecular quantum dot that, in turns, is driven by an auxiliary gate voltage. In the general context of (spin-)electronics, these results demonstrate that: (1) molecular quantum dots can be used as ultra-sensitive detectors for spin flip detection and (2) the use of
Atomic-scale Engineering of Magnetic Graphene Nanostructures
2019
Graphene can develop large magnetic moments in custom crafted open-shell nanostructures such as triangulene, a triangular piece of graphene with zigzag edges. Current methods of engineering graphene nano-systems on surfaces succeeded in producing atomically precise open-shell structures, but demonstration of their net spin remains elusive to date. Here, we fabricate triangulene-like graphene systems and demonstrate that they possess a spin S=1 ground state. Scanning tunnelling spectroscopy identifies the fingerprint of an underscreened S=1 Kondo state on this flakes at low temperatures, signaling the dominant ferromagnetic interactions between two spins. Combined with simulations based on the mean-field Hubbard model, we show that this S=1π-paramagnetism is robust, and can be manipulated to a weaker S=1/2 state by adding additional H-atoms to the radical sites, or by fabricating larger structures. The observation of a net magnetic moment in pure-carbon nanostructures opens promising...
Spintronics devices from bilayer graphene in contact to ferromagnetic insulators
Physical Review B, 2011
Graphene-based materials show promise for spintronic applications due to their potentially large spin coherence length. On the other hand, because of their small intrinsic spin-orbit interaction, an external magnetic source is desirable in order to perform spin manipulation. Because of the flat nature of graphene, the proximity interaction with a ferromagnetic insulator (FI) surface seems a natural way to introduce magnetic properties into graphene. Exploiting the peculiar electronic properties of bilayer graphene coupled with FIs, we show that it is possible to devise very efficient gate-tunable spin-rotators and spin-filters in a parameter regime of experimental feasibility. We also analyze the composition of the two spintronic building blocks in a spin-field-effect transistor. 72.80.Vp, 85.75.Mm, Graphene with its high mobility 1 and potentially long spin lifetimes, is an attractive material for spintronics. In particular, spin relaxation lengths on the order of micrometers have been observed 2 , together with spin relaxation times of hundreds of picoseconds, which are still believed to be limited by extrinsic impurities 3,4 . More recent experiments reported the measurement of a spin lifetime up to 1 ns in graphene and even of several nanoseconds in bilayer graphene (BG) 5,6 . Moreover, tunnel-injection of spin into graphene has been recently achieved using Co ferromagnets, with the observation of the largest non-local magnetoresistance of any material 7 . Graphene quantum dots have been also identified as an ideal host for spin qubits 8 .
Dual origin of defect magnetism in graphene and its reversible switching by molecular doping
Nature Communications, 2013
A possibility to control magnetic properties by using electric fields is one of the most desirable characteristics for spintronics applications. Finding a suitable material remains an elusive goal, with only a few candidates found so far. Graphene is one of them and offers a hope due to its weak spin-orbit interaction, the ability to control electronic properties by the electric field effect and the possibility to introduce paramagnetic centres such as vacancies and adatoms. Here we show that adatoms' magnetism in graphene is itinerant and can be controlled by doping, so that magnetic moments can be switched on and off. The much-discussed vacancy magnetism is found to have a dual origin, with two approximately equal contributions: one coming from the same itinerant magnetism and the other due to broken bonds. Our work suggests that graphene's magnetism can be controlled by the field effect, similar to its transport and optical properties, and that spin diffusion length can be significantly enhanced above a certain carrier density.
Graphene single-electron transistor as a spin sensor for magnetic adsorbates
Physical Review B, 2013
We study single electron transport through a graphene quantum dot with magnetic adsorbates. We focus on the relation between the spin order of the adsorbates and the linear conductance of the device. The electronic structure of the graphene dot with magnetic adsorbates is modeled through numerical diagonalization of a tight-binding model with an exchange potential. We consider several mechanisms by which the adsorbate magnetic state can influence transport in a single electron transistor: by tuning the addition energy, by changing the tunneling rate and, in the case of spin polarized electrodes, through magnetoresistive effects. Whereas the first mechanism is always present, the others require that the electrode has either an energy or spin dependent density of states. We find that graphene dots are optimal systems to detect the spin state of a few magnetic centers.
Tuning magnetoresistance in molybdenum disulphide and graphene using a molecular spin transition
Nature Communications
Coupling spins of molecular magnets to two-dimensional (2D) materials provides a framework to manipulate the magneto-conductance of 2D materials. However, with most molecules, the spin coupling is usually weak and devices fabricated from these require operation at low temperatures, which prevents practical applications. Here, we demonstrate field-effect transistors based on the coupling of a magnetic molecule quinoidal dithienyl perylenequinodimethane (QDTP) to 2D materials. Uniquely, QDTP switches from a spin-singlet state at low temperature to a spin-triplet state above 370 K, and the spin transition can be electrically transduced by both graphene and molybdenum disulphide. Graphene-QDTP shows hole-doping and a large positive magnetoresistance (~50%), while molybdenum disulphide-QDTP demonstrates electron-doping and a switch to large negative magnetoresistance (~100%) above the magnetic transition. Our work shows the promise of spin detection at high temperature by coupling 2D materials and molecular magnets.
Multiple Spin State Analysis of Magnetic Nano Graphene
Journal of the Magnetics Society of Japan, 2011
Recent experiments indicate room-temperature ferromagnetism in graphite-like materials. This paper offers multiple spin state analysis applied to asymmetric graphene molecule to find out mechanism of ferromagnetic nature. First principle density functional theory is applied to calculate spin density, energy and atom position depending on each spin state. Molecules with dihydrogenated zigzag edges like C64H27, C56H24, C64H25, C56H22 and C64H23 show that in every molecule the highest spin state is the most stable one with over 3000 K energy difference with next spin state. This result suggests a stability of room temperature ferromagnetism in these molecules. In contrast, nitrogen substituted molecules like C59N5H22, C52N4H20, C61N3H22, C54N2H20 and C63N1H22 show opposite result that the lowest spin state is the most stable. Magnetic stability of graphene molecule can be explained by three key issues, that is, edge specified localized spin density, parallel spins exchange interaction inside of a molecule and atom position optimization depending on spin state. Those results will be applied to design a carbon-base ferro-magnet, an ultra high density 100 tera bit /inch 2 class information storage and spintronic devices.
Graphene-multiferroic interfaces for spintronics applications
Scientific Reports, 2016
Graphene and magnetoelectric multiferroics are promising materials for spintronic devices with high performance and low energy consumption. A very long spin diffusion length and high carrier mobility make graphene attractive for spintronics. The coupling between ferroelectricity and magnetism, which characterises magnetoelectrics, opens the way towards unique device architectures. In this work, we combine the features of both materials by investigating the interface between graphene and BaMnO 3 , a magnetoelectric multiferroic. We show that electron charge is transferred across the interface and magnetization is induced in the graphene sheet due to the strong interaction between C and Mn. Depending on the relative orientation of graphene and BaMnO 3 , a quasi-half-metal or a magnetic semiconductor can be obtained. A remarkably large proximity induced spin splitting of the Dirac cones (~300 meV) is achieved. We also show how doping with acceptors can make the high-mobility region of the electronic bands experimentally accessible. This suggests a series of possible applications in spintronics (e.g. spin filters, spin injectors) for hybrid organic-multiferroic materials and reveals hybrid organic-multiferroics as a new class of materials that may exhibit exotic phenomena such as the quantum anomalous Hall effect and a Rashba spin-orbit induced topological gap.