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1.
Science ; 366(6469): 1107-1110, 2019 11 29.
Artigo em Inglês | MEDLINE | ID: mdl-31780554

RESUMO

Robustly coherent spin centers that can be integrated into devices are a key ingredient of quantum technologies. Vacancies in semiconductors are excellent candidates, and theory predicts that defects in conjugated carbon materials should also display long coherence times. However, the quantum performance of carbon nanostructures has remained stunted by an inability to alter the sp2-carbon lattice with atomic precision. Here, we demonstrate that topological tailoring leads to superior quantum performance in molecular graphene nanostructures. We unravel the decoherence mechanisms, quantify nuclear and environmental effects, and observe spin-coherence times that outclass most nanomaterials. These results validate long-standing assumptions on the coherent behavior of topological defects in graphene and open up the possibility of introducing controlled quantum-coherent centers in the upcoming generation of carbon-based optoelectronic, electronic, and bioactive systems.

2.
Chem Sci ; 9(45): 8474-8481, 2018 Dec 07.
Artigo em Inglês | MEDLINE | ID: mdl-30568771

RESUMO

We present the design, synthesis and magnetic properties of molecular magnetic systems that contain all elements necessary for spin-valve control in molecular spintronic devices in a single molecule. We investigate the static and dynamic magnetic properties and quantum spin properties of butadiyne-linked homo- and hetero-nuclear lanthanide-porphyrin dimers. A heterometallated porphyrin dimer containing both TbIII and DyIII centres is created rationally by the stepwise oxidative homocoupling of distinct lanthanide-porphyrin monomers. TbIII and DyIII mononuclear porphyrin complexes, homodimers and heterodimers all exhibit slow magnetic relaxation below 10 kelvin under a static magnetic field. The coherence times for GdIII porphyrin monomers and dimers are found to be in excess of 3.0 µs at 2 K, allowing distinct magnetic manipulations in low temperature transport experiments.

3.
Nature ; 557(7707): 691-695, 2018 05.
Artigo em Inglês | MEDLINE | ID: mdl-29849157

RESUMO

Graphene, a single-layer network of carbon atoms, has outstanding electrical and mechanical properties 1 . Graphene ribbons with nanometre-scale widths2,3 (nanoribbons) should exhibit half-metallicity 4 and quantum confinement. Magnetic edges in graphene nanoribbons5,6 have been studied extensively from a theoretical standpoint because their coherent manipulation would be a milestone for spintronic 7 and quantum computing devices 8 . However, experimental investigations have been hampered because nanoribbon edges cannot be produced with atomic precision and the graphene terminations that have been proposed are chemically unstable 9 . Here we address both of these problems, by using molecular graphene nanoribbons functionalized with stable spin-bearing radical groups. We observe the predicted delocalized magnetic edge states and test theoretical models of the spin dynamics and spin-environment interactions. Comparison with a non-graphitized reference material enables us to clearly identify the characteristic behaviour of the radical-functionalized graphene nanoribbons. We quantify the parameters of spin-orbit coupling, define the interaction patterns and determine the spin decoherence channels. Even without any optimization, the spin coherence time is in the range of microseconds at room temperature, and we perform quantum inversion operations between edge and radical spins. Our approach provides a way of testing the theory of magnetism in graphene nanoribbons experimentally. The coherence times that we observe open up encouraging prospects for the use of magnetic nanoribbons in quantum spintronic devices.

4.
Nature ; 561(7723): E31, 2018 09.
Artigo em Inglês | MEDLINE | ID: mdl-29946171

RESUMO

In Fig. 1 of this Letter, there should have been two nitrogen (N) atoms at the 1,3-positions of all the blue chemical structures (next to the oxygen atoms), rather than one at the 2-position. The figure has been corrected online, and the original incorrect figure is shown as Supplementary Information to the accompanying Amendment.

5.
Phys Rev Lett ; 119(14): 147701, 2017 Oct 06.
Artigo em Inglês | MEDLINE | ID: mdl-29053322

RESUMO

Coupling between a crystal of di(phenyl)-(2,4,6-trinitrophenyl)iminoazanium radicals and a superconducting microwave resonator is investigated in a circuit quantum electrodynamics (circuit QED) architecture. The crystal exhibits paramagnetic behavior above 4 K, with antiferromagnetic correlations appearing below this temperature, and we demonstrate strong coupling at base temperature. The magnetic resonance acquires a field angle dependence as the crystal is cooled down, indicating anisotropy of the exchange interactions. These results show that multispin modes in organic crystals are suitable for circuit QED, offering a platform for their coherent manipulation. They also utilize the circuit QED architecture as a way to probe spin correlations at low temperature.

6.
Inorg Chem ; 56(9): 4911-4917, 2017 May 01.
Artigo em Inglês | MEDLINE | ID: mdl-28414438

RESUMO

Controlling the coordination sphere of lanthanoid complexes is a challenging critical step toward controlling their relaxation properties. Here we present the synthesis of hexacoordinated dysprosium single-molecule magnets, where tripodal ligands achieve a near-perfect octahedral coordination. We perform a complete experimental and theoretical investigation of their magnetic properties, including a full single-crystal magnetic anisotropy analysis. The combination of electrostatic and crystal-field computational tools (SIMPRE and CONDON codes) allows us to explain the static behavior of these systems in detail.

7.
Nat Mater ; 15(2): 164-8, 2016 Feb.
Artigo em Inglês | MEDLINE | ID: mdl-26641019

RESUMO

Controlling the dynamics of spins on surfaces is pivotal to the design of spintronic and quantum computing devices. Proposed schemes involve the interaction of spins with graphene to enable surface-state spintronics and electrical spin manipulation. However, the influence of the graphene environment on the spin systems has yet to be unravelled. Here we explore the spin-graphene interaction by studying the classical and quantum dynamics of molecular magnets on graphene. Whereas the static spin response remains unaltered, the quantum spin dynamics and associated selection rules are profoundly modulated. The couplings to graphene phonons, to other spins, and to Dirac fermions are quantified using a newly developed model. Coupling to Dirac electrons introduces a dominant quantum relaxation channel that, by driving the spins over Villain's threshold, gives rise to fully coherent, resonant spin tunnelling. Our findings provide fundamental insight into the interaction between spins and graphene, establishing the basis for electrical spin manipulation in graphene nanodevices.

8.
Faraday Discuss ; 185: 347-59, 2015.
Artigo em Inglês | MEDLINE | ID: mdl-26470791

RESUMO

We report the synthesis and magnetic and photomagnetic behaviour of a novel valence tautomeric cobalt complex, [Co(3,5-dbbq)2(µ-bpym)] (1) (3,5-dbbq = 3,5-di-tert-butyl-1,2-benzoquinone and µ-bpym = 2,2'-bipyrimidine). The synthesis is performed by reacting Co2(CO)8 and µ-bpym in the presence of the ligand 3,5-dbbq in a mixed solvent under inert atmosphere. The magnetic behavior clearly shows the presence of electron transfer from the catecholate ligand to the cobalt center, producing valence tautomers of [Co(II)(SQ)2] with a transition temperature (T1/2) of 215 K. Photomagnetic studies, performed via both SQUID magnetometry and X-band electron paramagnetic resonance, show the clear presence of photoinduced valence tautomerism, at temperatures considerably higher than previous systems. A metastable charge distribution is observed, strengthening previous investigations on the character of mixed valence ligands. Entropy-driven valence tautomeric interconversion is observed, and drives the transition to the most stable charge distribution. The complex has the ability to coordinate and can be used as a photoswitchable building block, with the photomagnetic characterisation evidencing a metastable state lifetime of the photo-induced valence tautomeric process of ca. 2.9 × 10(4) s below 20 K. The observed yields are higher than ones in similar systems, showing that tiny changes in the molecular structures may have a huge impact.

10.
J Am Chem Soc ; 137(40): 12923-8, 2015 Oct 14.
Artigo em Inglês | MEDLINE | ID: mdl-26352187

RESUMO

The high-spin (S = 1) tetrahedral Ni(II) complex [Ni{(i)Pr2P(Se)NP(Se)(i)Pr2}2] was investigated by magnetometry, spectroscopic, and quantum chemical methods. Angle-resolved magnetometry studies revealed the orientation of the magnetization principal axes. The very large zero-field splitting (zfs), D = 45.40(2) cm(-1), E = 1.91(2) cm(-1), of the complex was accurately determined by far-infrared magnetic spectroscopy, directly observing transitions between the spin sublevels of the triplet ground state. These are the largest zfs values ever determined--directly--for a high-spin Ni(II) complex. Ab initio calculations further probed the electronic structure of the system, elucidating the factors controlling the sign and magnitude of D. The latter is dominated by spin-orbit coupling contributions of the Ni ions, whereas the corresponding effects of the Se atoms are remarkably smaller.

11.
Nano Lett ; 15(8): 4942-7, 2015 Aug 12.
Artigo em Inglês | MEDLINE | ID: mdl-26218205

RESUMO

To study the magnetic dynamics of superparamagnetic nanoparticles, we use scanning probe relaxometry and dephasing of the nitrogen vacancy (NV) center in diamond, characterizing the spin noise of a single 10 nm magnetite particle. Additionally, we show the anisotropy of the NV sensitivity's dependence on the applied decoherence measurement method. By comparing the change in relaxation (T1) and dephasing (T2) time in the NV center when scanning a nanoparticle over it, we are able to extract the nanoparticle's diameter and distance from the NV center using an Ornstein-Uhlenbeck model for the nanoparticle's fluctuations. This scanning probe technique can be used in the future to characterize different spin label substitutes for both medical applications and basic magnetic nanoparticle behavior.

12.
Adv Mater ; 27(16): 2635-41, 2015 Apr 24.
Artigo em Inglês | MEDLINE | ID: mdl-25787669

RESUMO

The response of individual domains in wafer-sized chemical vapor deposition graphene is measured by contactless sub-terahertz interferometry, observing the intrinsic optical conductance and reaching very high mobility values. It is shown that charged scatterers limit the mobility, validating previous theoretical predictions, and sub-terahertz quality assessment is demonstrated, as necessary for large-scale applications in touchscreens, as well as wearable and optoelectronic devices.


Assuntos
Grafite/química , Cobre/química , Interferometria/métodos , Polimetil Metacrilato/química , Espalhamento de Radiação , Dióxido de Silício/química , Análise Espectral/métodos , Temperatura Ambiente
13.
Phys Chem Chem Phys ; 16(34): 18076-82, 2014 Sep 14.
Artigo em Inglês | MEDLINE | ID: mdl-25072189

RESUMO

Molecular magnetism is considered an area where magnetic phenomena that are usually difficult to demonstrate can emerge with particular clarity. Over the years, however, less understandable systems have appeared in the literature of molecular magnetic materials, in some cases showing features that hint at the spontaneous emergence of global structures out of local interactions. This ingredient is typical of a wider class of problems, called complex behaviours, where the theory of complexity is currently being developed. In this perspective we wish to focus our attention on these systems and the underlying problematic that they highlight. We particularly highlight the emergence of the signatures of complexity in several molecular magnetic systems, which may provide unexplored opportunities for physical and chemical investigations.

14.
Dalton Trans ; 43(11): 4220-32, 2014 Mar 21.
Artigo em Inglês | MEDLINE | ID: mdl-24514949

RESUMO

We discuss current developments in the synthesis and characterization of magnetic nanohybrids made of molecular magnets and nanostructured materials. We first review several novel approaches that have recently been attempted to combine magnetic coordination complexes with differently-obtained inorganic systems. Special focus is placed on how the altered environment can affect the magnetic properties of single molecules, providing new routes to multifunctional devices based on hybrid magnetic nanosystems. We then show how this approach is opening new outlooks towards the control of nanomagnets using external stimuli (e.g. photons, electrons, etc.) and for the creation of ultra-sensitive devices. Eventually we provide a unified vision of the area, with a personal perspective on the main goals currently at stake and of possible future developments.

15.
Nat Mater ; 12(3): 202-6, 2013 Mar.
Artigo em Inglês | MEDLINE | ID: mdl-23202373

RESUMO

Controlling the speed at which systems evolve is a challenge shared by all disciplines, and otherwise unrelated areas use common theoretical frameworks towards this goal. A particularly widespread model is Glauber dynamics, which describes the time evolution of the Ising model and can be applied to any binary system. Here we show, using molecular nanowires under irradiation, that Glauber dynamics can be controlled by a novel domain-wall kickoff mechanism. In contrast to known processes, the kickoff has unambiguous fingerprints, slowing down the spin-flip attempt rate by several orders of magnitude, and following a scaling law. The required irradiance is very low, a substantial improvement over present methods of magneto-optical switching. These results provide a new way to control and study stochastic dynamic processes. Being general for Glauber dynamics, they can be extended to different kinds of magnetic nanowires and to numerous fields, ranging from social evolution to neural networks and chemical reactivity.

16.
Inorg Chem ; 50(13): 6114-21, 2011 Jul 04.
Artigo em Inglês | MEDLINE | ID: mdl-21657207

RESUMO

We demonstrate the use of a Cu(I) catalyzed "Click" reaction in the synthesis of novel ligands for spin crossover complexes. The reaction between azides and alkynes was used to synthesize the reported tripodal ligand tris[(1-benzyl-1H-1,2,3-triazol-4-yl)methyl]amine, TBTA, and the new ligands tris[(1-cyclohexyl-1H-1,2,3-triazol-4-yl)methyl]amine, TCTA, and tris[(1-n-butyl-1H-1,2,3-triazol-4-yl)methyl]amine, TBuTA. Reactions of TBTA with Co(ClO(4))(2) lead to complexes of the form [Co(TBTA)(CH(3)CN)(3)](ClO(4))(2), 1, and [Co(TBTA)(2)](ClO(4))(2), 2, where complex formation can be controlled by the metal/ligand ratio and the complexes 1 and 2 can be chemically and reversibly switched from one form to another in solution resulting in coordination ambivalence. The benzyl substituents of TBTA in 2 show intramolecular C-H-π T-stacking that generates a chemical pressure to stabilize the low spin (LS) state at lower temperatures. The structural parameters of 2 are consistent with a Jahn-Teller active LS Co(II) (elongation) ion showing four short and two long bonds. 2 shows spin-crossover (SCO) behavior in the solid state and in solution with a high T(0) close to room temperature which is driven by the T-stacking. 1 remains high spin (HS) between 2 and 400 K. Reversible chemical switching is observed between 1 and 2 at room temperature, with an accompanying change in the spin state from HS to LS. The importance of the intramolecular T-stacking in driving the SCO behavior is proven by comparison with two analogous compounds that lack an aromatic substituent and remain HS down to very low temperatures.


Assuntos
Cobalto/química , Compostos Organometálicos/química , Alquinos/química , Azidas/química , Catálise , Química Click , Cobre/química , Cristalografia por Raios X , Ligantes , Modelos Moleculares , Estrutura Molecular , Compostos Organometálicos/síntese química , Estereoisomerismo
19.
J Am Chem Soc ; 131(42): 15143-51, 2009 Oct 28.
Artigo em Inglês | MEDLINE | ID: mdl-19799421

RESUMO

A new heteroleptic bis(phthalocyaninato) terbium(III) complex 1, bearing a pyrenyl group, exhibits temperature and frequency dependence of ac magnetic susceptibility, typical of single-molecule magnets. The complex was successfully attached to single-walled carbon nanotubes (SWNTs) using pi-pi interactions, yielding a 1-SWNT conjugate. The supramolecular grafting of 1 to SWNTs was proven qualitatively and quantitatively by high-resolution transmission electron microscopy, emission spectroscopy, and atomic force spectroscopy. Giving a clear magnetic fingerprint, the anisotropy energy barrier and the magnetic relaxation time of the 1-SWNT conjugate are both increased in comparison with the pure crystalline compound 1, likely due to the suppression of intermolecular interactions. The obtained results propose the 1-SWNT conjugate as a promising constituent unit in magnetic single-molecule measurements using molecular spintronics devices.

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