Bulletin of the American Physical Society
APS March Meeting 2016
Volume 61, Number 2
Monday–Friday, March 14–18, 2016; Baltimore, Maryland
Session F21: Molecular NanomagnetsFocus
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Sponsoring Units: GMAG DMP Chair: Andrew Kent, New York University Room: 320 |
Tuesday, March 15, 2016 11:15AM - 11:51AM |
F21.00001: Coherent manipulation of quantum spin states in a single molecular nanomagnet Invited Speaker: Wolfgang Wernsdorfer The endeavour of quantum electronics is driven by one of the most ambitious technological goals of today's scientists: the realization of an operational quantum computer (\underline {http://qurope.eu}). We started to address this goal by the new research field of molecular quantum spintronics. The building blocks are magnetic molecules, i.e. well-defined spin qubits. We will discuss this still largely unexplored field and present our first results: For example, using a molecular spin-transistor, we achieved the electronic read-out of the nuclear spin of an individual metal atom embedded in an SMM. We could show very long spin lifetimes (\textgreater 10 s). Using the hyperfine Stark effect, which transforms electric fields into local effective magnetic fields, we could not only tune the resonance frequency by several MHz, but also perform coherent quantum manipulations on a single nuclear qubit faster than a $\mu $s by means of electrical fields only, establishing the individual addressability of identical nuclear qubits. Using three different microwave frequencies, we could implement a simple four-level Grover algorithm. S. Thiele, F. Balestro, R. Ballou, S. Klyatskaya, M. Ruben, W. Wernsdorfer, Science 344, 1135 (2014). [Preview Abstract] |
Tuesday, March 15, 2016 11:51AM - 12:03PM |
F21.00002: Landau-Zener in a continuously measured molecular spin Filippo Troiani, Marco Affronte, Stephan Thiele, Clement Godfrin, Franck Balestro, Wolfgang Wernsdorfer, Svetlana Klyatskaya, Mario Ruben The dynamics of a quantum system driven through an avoided level crossing represernts a relevant problem in many physical contexts. Here we present a joint theoretical and experimental investigation of a single-molecule magnet (namely, a terbium double-decker complex) in a three-terminal geometry. The Tb spin is driven through an avoided level crossing by a time-dependent magnetic field, and its dynamics is monitored through a continuous measurement of the conductance. The dependence of the spin-reversal probability on the field sweeping rate presents clear deviations from the Landau-Zener formula, which applies to the case of closed systems. The comparison between direct and inverse Landau-Zener transitions points at the dominance of dephasing, with respect to inelastic incoherent processes. The spin dynamics is simulated within a master equation approach. The observed behaviors are reproduced by assuming that dephasing takes place in the basis of the time-dependent Hamiltonian eigenstates. The spin dephasing is traced back to the continuous measurement of the electron spin, and a fundamental role is played by the finite time resolution of the conductance measurement. [Preview Abstract] |
Tuesday, March 15, 2016 12:03PM - 12:15PM |
F21.00003: Magnetic hysteresis in a lanthanide molecular magnet dimer system James Atkinson, Rebecca Cebulka, Enrique del Barco, Olivier Roubeau, Veronica Velasco, Leo Barrios, Guillem Aromi Molecular magnets present a wonderful means for studying the dynamics of spin. Often synthesized as a crystal lattice of identical systems, ensemble measurements enable thorough detailing of the internal degrees of freedom. Here we present the results of characterization performed on a dimer system, CeTm(HL)$_{2}$(H$_{2}$L)NO$_{3}$pyH$_{2}$O (L = ligand, C$_{45}$H$_{31}$O$_{15}$N$_{3}$), consisting of two lanthanide spins (Cerium and Thulium) with expected local axial anisotropies tilted with respect to each other. Microwave EPR spectroscopy at low temperature reveals hysteresis in observed absorption features, with angle dependence studies indicating the presence of several “easy axis” orientations. We attempt to understand this system through modelling via a spin Hamiltonian, and to determine the strength and nature of the coupling between the lanthanide centers. [Preview Abstract] |
Tuesday, March 15, 2016 12:15PM - 12:27PM |
F21.00004: Search for giant magnetic anisotropy in transition-metal dimers on defected hexagonal boron nitride sheet Jie Li, Hui Wang, Jun Hu, Ruqian Wu For a magnetic units at the nanometer scale, one of the most important issues is how to hold thermal fluctuation of its magnetization, i.e., how to enhance its blocking temperature (T$_{\mathrm{\$ \mathunderscore B\$ }})$ to above 300K. Through systematic density functional calculations, the structural stability and magnetic properties of many transition-metal dimers embedded in a defected hexagonal boron nitride monolayer are investigated. We find twelve cases that may have magnetic anisotropy energies (MAEs) larger than 30 meV. In particular, Ir-Ir@Dh-BN has both large MAE (\textasciitilde 126 meV) and high structural stability, which makes it a promising candidate of magnetic unit in spintronics and quantum computing devices. [Preview Abstract] |
Tuesday, March 15, 2016 12:27PM - 12:39PM |
F21.00005: Molecular Magnetism in MnTe Clusters Jia Chen, Arun Nanduri, Bonnie Choi, Andrew Millis, David Reichman, Xavier Roy Electron correlation in recently synthesized molecular clusters with Mn$_4$Te$_4$ cores in cubane structures and ligand exteriors are studied experimentally and theoretically. We used density functional theory with on-site Coulomb interactions (DFT+U) to construct effective spin Hamiltonians and estimate the dependence of parameters on choice of ligand. The lack of inversion symmetry combined with the heavy tellurium ions leads to a significant Dzyaloshinskii-Moriya (DM) interaction. Comparison of measurements to the magnetic susceptibility calculated from the spin model is used to validate the results. We also extend this work to more complex clusters with more than one cubanes, where interesting high-spin ground state may occur. It has been measured recently, Fe$_8$Te$_8$ in dicubane structure has ground state with magnetization of12$\mu_B$, which makes it promising candidate for single molecular magnets. [Preview Abstract] |
Tuesday, March 15, 2016 12:39PM - 12:51PM |
F21.00006: \textbf{Spin-Valve Effect at Organic-Ferromagnetic Interfaces} Nicolae Atodiresei, Vasile Caciuc, Stefan Bl\"ugel The ability to reliably describe the electronic properties of carbon-based materials adsorbed on magnetic surfaces is essential to understand and assist the engineering of functionalities in hybrid organic spintronic devices. Based on the density functional theory, we performed theoretical studies [1-4] to understand how to tailor the magnetic properties of hybrid organic-ferromagnetic interfaces by adsorbing organic materials containing $\pi $-electrons onto several magnetic substrates. For such hybrid systems, the magnetic properties like molecular magnetic moments and their spatial orientation, spin-polarization and the magnetic exchange coupling can be specifically tuned by an appropriate choice of the organic material. *Email: n.atodiresei@fz-juelich.de [1] N. Atodiresei et al., MRS Bulletin 39, 596 (2014). [2] J. Brede et al., Nat. Nanotech. 9, 1018 (2014). [3] K. V. Raman et al., Nature 493, 509 (2013). [4] M. Callsen et al., Phys. Rev. Lett. 111, 106805 (2013). [Preview Abstract] |
Tuesday, March 15, 2016 12:51PM - 1:03PM |
F21.00007: Magnetic dipole-dipole sensing at atomic scale using electron spin resonance STM T. Choi, W. Paul, S. Rolf-Pissarczyk, A. Macdonald, K. Yang, F.D. Natterer, C.P. Lutz, A.J. Heinrich Magnetometry having both high magnetic field sensitivity and atomic resolution has been an important goal for applications in diverse fields covering physics, material science, and biomedical science. Recent development of electron spin resonance STM (ESR-STM) promises coherent manipulation of spins and studies on magnetic interaction of artificially built nanostructures, leading toward quantum computation, simulation, and sensors In ESR-STM experiments, we find that the ESR signal from an Fe atom underneath a STM tip splits into two different frequencies when we position an additional Fe atom nearby. We measure an ESR energy splitting that decays as 1/r$^{\mathrm{3}}$ (r is the separation of the two Fe atoms), indicating that the atoms are coupled through magnetic dipole-dipole interaction. This energy and distance relation enables us to determine magnetic moments of atoms and molecules on a surface with high precision in energy. Unique and advantageous aspects of ESR-STM are the atom manipulation capabilities, which allow us to build atomically precise nanostructures and examine their interactions. For instance, we construct a dice \textit{cinque} arrangement of five Fe atoms, and probe their interaction and energy degeneracy. We demonstrate the ESR-STM technique can be utilized for quantum magnetic sensors. [Preview Abstract] |
Tuesday, March 15, 2016 1:03PM - 1:15PM |
F21.00008: ABSTRACT WITHDRAWN |
Tuesday, March 15, 2016 1:15PM - 1:27PM |
F21.00009: Spin blockade effect in single-molecule transistors Guangpu Luo, Kyungwha Park Recently single-molecule transistors consisting of individual single-molecule magnets trapped between electrodes have been experimentally realized and electron transport properties through individual single-molecule magnets have been measured. For a single-molecule magnet the (2S+1)-fold degeneracy of magnetic levels in a given spin multiplet is lifted even in the absence of external magnetic field, due to the magnetic anisotropy induced by spin-orbit coupling. This anisotropic nature of single-molecule magnets allowed one to discover interesting, unexpected transport properties. A recent theoretical study showed that an Eu-based anisotropic magnetic molecule can switch its magnetic anisotropy between magnetic easy plane and easy axis upon varying the charge state of the molecule. Motivated by this report, we investigate how this switch of magnetic anisotropy influences the electron transport through the molecule, by considering sequential electron tunneling. We calculate current-voltage characteristics by solving the master equation based on the model Hamiltonians. We explore this interesting effect in the absence and presence of external magnetic field. [Preview Abstract] |
Tuesday, March 15, 2016 1:27PM - 1:39PM |
F21.00010: Hybrid quantum systems with YBCO coplanar resonators and spin ensembles of organic radicals Alberto Ghirri, Claudio Bonizzoni, Filippo Troiani, Antonio Cassinese, Massimiliano D'Arienzo, Luca Beverina, Marco Affronte We have studied the coherent coupling of microwave photons in a superconducting coplanar resonator with a spin ensemble of stable open-shell organic radicals. We fabricated YBCO/sapphire coplanar resonators that show quality factors $\simeq $ 3*10\textasciicircum 4 at 1.8 K, that remain remarkably stable in high magnetic field applied parallel to the YBCO film [QL (7 T) $=$ 90{\%} QL (0 T)] [1]. Spin ensembles of (3,5-Dichloro-4-pyridyl)bis(2,4,6-trichlorophenyl)methyl organic radical (PyBTM) show sharp EPR linewidth (8 MHz) due to the effect of the exchange narrowing. The frequency of the spin transition is tuned by means of the external magnetic field. We show the achievement of the strong collective coupling with the resonant photons with coupling rates exceeding 90 MHz at 1.8 K. [1] A. Ghirri, C. Bonizzoni, D. Gerace, S. Sanna, A. Cassinese and M. Affronte, Appl. Phys. Lett. 106, 184101 (2015). [Preview Abstract] |
Tuesday, March 15, 2016 1:39PM - 1:51PM |
F21.00011: First-principles study on magnetism of Ru monolayer under an external electric field Yukie Kitaoka, Hiroshi Imamura Electric field control of magnetic properties such as magnetic moment and magnetic anisotropy has been attracted. For the 4$d$ TM films, on the other hand, it was recently reported that the ferromagnetism Pd thin-film is induced by application of an external electric field otherwise Pd thin-film shows paramagnetic [1]. However, little attention has been paid to the magnetism of other 4$d$ TMs. Here, we investigate the magnetism of the free-standing Ru monolayer and that on MgO(001) substrate under an external electric field by using first-principles FLAPW method [2]. We found that the free-standing Ru monolayer is ferromagnet with magnetic moment of 1.50 $¥mu_B$/atom. The MA energy is 3.45 meV/atom, indicating perpendicular MA, at zero electric field ($E$=0) and increases up to 3.84 meV/atom by application of $E$=1 (V/{¥AA}). The Ru monolayer on MgO(001) substrate is also ferromagnet with magnetic moment of 0.89 $¥mu_B$/atom. The MA energy is 1.49 meV/atom, indicating perpendicular MA, at $E$=0 and decreases to 1.33 meV/atom by application of $E$=1 (V/{¥AA}). [1] Y. Sun, J. D. Burton, E. Y. Tsymbal, PRB 81, 064413 (2010). [2] K. Nakamura, T. Ito, A. J. Freeman, L. Zhong, J. Fernandez-de-Castro, PRB, 67, 014420 (2003). [Preview Abstract] |
Tuesday, March 15, 2016 1:51PM - 2:03PM |
F21.00012: Chemically Controllable Ferromagnetic Graphene for High-Performance Spintronic Devices~ Jeongmin Hong The spin and charge of the electron when taken together, offer many opportunities for the creation of new information processing and storage devices applications with ultralow power consumption. Chemically controllable growth of large area nanocarbon structures has attracted considerable interests due to their superior properties. If large area nanocarbon could have by-design magnetic properties, multifunctional electronic devices could be built through modulation controlled by external factors such as 1) functionalization onto basal plane of carbon, 2) substrates effects (proximity induced ferromagnetism), and 3) external electric field. We performed soft X-ray measurement techniques using X-ray magnetic circular dichroism (XMCD) and revealed the controllable ferromagnetic properties on graphene structures. The chemically controllable nanomagnet would be an excellent building block for the applications of graphene-based high-performance spintronic devices.~ [Preview Abstract] |
Tuesday, March 15, 2016 2:03PM - 2:15PM |
F21.00013: Energy gap of Graphene Nanoflakes: Edge Magnetism and Self-Energy Corrections. Romeo De Coss Gomez, Carlos Manuel Ramos Castillo Previous theoretical works has predicted that graphene nanostructures with zigzag edge exhibit metallic behavior around 6-7 nm, however in such calculations the magnetic nature of zigzag edges was not considered. In this work, the influence of the edge magnetism on the size dependence of energy-gap in hexagonal gaphene nanoflakes (GNFs) with zigzag borders is studied by density functional theory calculations. Thus, we found that meanwhile the calculations without spin polarization predicts that the metallic behaviour for GNFs begin at 6 nm deviating from the trend predicted for effective model of Dirac fermions, spin-polarized calculations predicts semiconducting behavior at 6 nm. This result shows clearly that the origin of metallic behaviour predicted at 6 nm in previous works is not related with the well known band-gap problem of Kohn-Sham scheme, but with neglecting spin polarization. Furthermore, to correct the band-gap problem of Kohn-Sham Scheme, we have calculated the size dependence of fundamental energy-gap using the quasiparticle formalism by adding/removing an electron to/from the system. [Preview Abstract] |
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