Publications (221) View all
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Article: Spin dynamics of molecular nanomagnets fully unraveled by four-dimensional inelastic neutron scattering
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ABSTRACT: Molecular nanomagnets are among the first examples of spin systems of finite size and have been test-beds for addressing a range of elusive but important phenomena in quantum dynamics. In fact, for short-enough timescales the spin wavefunctions evolve coherently according to the an appropriate cluster spin-Hamiltonian, whose structure can be tailored at the synthetic level to meet specific requirements. Unfortunately, to this point it has been impossible to determine the spin dynamics directly. If the molecule is sufficiently simple, the spin motion can be indirectly assessed by an approximate model Hamiltonian fitted to experimental measurements of various types. Here we show that recently-developed instrumentation yields the four-dimensional inelastic-neutron scattering function S(Q,E) in vast portions of reciprocal space and enables the spin dynamics to be determined with no need of any model Hamiltonian. We exploit the Cr8 antiferromagnetic ring as a benchmark to demonstrate the potential of this new approach. For the first time we extract a model-free picture of the quantum dynamics of a molecular nanomagnet. This allows us, for example, to examine how a quantum fluctuation propagates along the ring and to directly test the degree of validity of the N\'{e}el-vector-tunneling description of the spin dynamics.08/2012; -
Article: Chemical engineering of molecular qubits.
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ABSTRACT: We show that the electron spin phase memory time, the most important property of a molecular nanomagnet from the perspective of quantum information processing, can be improved dramatically by chemically engineering the molecular structure to optimize the environment of the spin. We vary systematically each structural component of the class of antiferromagnetic Cr(7)Ni rings to identify the sources of decoherence. The optimal structure exhibits a phase memory time exceeding 15 μs.Physical Review Letters 03/2012; 108(10):107204. · 7.37 Impact Factor -
Article: Inelastic neutron scattering studies on the odd-membered antiferromagnetic wheel Cr8Ni
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ABSTRACT: [((C3H7)-C-i)(2)NH2][Cr8NiF9(O2CCMe)(18)], or Cr8Ni, is a prominent example of an odd-membered antiferromagnetic "wheel." A detailed characterization of the magnetic properties of Cr8Ni has been conducted. Inelastic neutron scattering (INS) is used to investigate the energy and momentum transfer dependence of the low-lying spin excitations, including excited states inaccessible by other experimental techniques. The richness of the INS data, in conjunction with microscopic spin Hamiltonian simulations, enables an accurate characterization of the magnetic properties of Cr8Ni. Nearest-neighbor exchange constants of J(CrCr) = 1.31 meV and J(CrNi) = 3.22 meV are determined, and clear evidence of axial single-ion anisotropy is found. The parameters determined by INS are shown to fit magnetic susceptibility. The spectroscopic identification of several successive S = 1 excited total spin states and lowest spin band excitations show that the rotational band picture, valid for bipartite AFM wheels, breaks down for this odd-numbered wheel. The exchange constants determined here differ from previous efforts based on bulk measurements, and possible reasons are discussed. The large J(CrNi)/J(CrCr) ratio in Cr8Ni puts this wheel into a regime with strong quantum fluctuations in which the ground state can be described with a valence bond solid state picture.Physical Review B. 01/2012; 86(6). -
Article: Spin entanglement in supramolecular systems
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ABSTRACT: Entanglement is an intriguing property of quantum systems that is essential for the implementation of quantum information processing. We review recent results on the establishment of magnetic coupling and spin entanglement between molecular clusters of Cr7Ni antiferromagnetic rings. We firstly present the magnetic features of the molecular building blocks and the strategy to link them without altering their properties. A systematic study of the magnetic interaction in (Cr7Ni)2 dimers through different heteroaromatic linkers is then reported. Finally, for the dimer with strongest coupling, the entanglement is directly investigated both theoretically and experimentally.Journal of Physics Conference Series 07/2011; 303(1):012033. -
Article: Observation of a level crossing in a molecular nanomagnet using implanted muons.
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ABSTRACT: We have observed an electronic energy level crossing in a molecular nanomagnet (MNM) using muon spin relaxation. This effect, not observed previously despite several muon studies of MNM systems, provides further evidence that the spin relaxation of the implanted muon is sensitive to the dynamics of the electronic spin. Our measurements on a broken ring MNM [H(2)N(t)Bu(is)Pr][Cr(8)CdF(9)(O(2)CC(CH(3))(3))(18)], which contains eight Cr ions, show clear evidence for the S = 0 --> S = 1 transition that takes place at B(c) = 2.3 T. The crossing is observed as a resonance-like dip in the average positron asymmetry and also in the muon spin relaxation rate, which shows a sharp increase in magnitude at the transition and a peak centred within the S = 1 regime.Journal of Physics Condensed Matter 06/2011; 23(24):242201. · 2.55 Impact Factor
