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Spin dynamics of molecular nanomagnets unravelled at atomic scale by four-dimensional inelastic neutron scattering

Abstract

Molecular nanomagnets are among the first examples of finite-size spin systems and have been test beds for addressing several phenomena in quantum dynamics. In fact, for short-enough timescales the spin wavefunctions evolve coherently according to an appropriate spin Hamiltonian, which can be engineered to meet specific requirements. Unfortunately, so far it has been impossible to determine these spin dynamics directly. Here we show that recently developed instrumentation yields the four-dimensional inelastic-neutron scattering function in vast portions of reciprocal space and enables the spin dynamics to be determined directly. We use the Cr8 antiferromagnetic ring as a benchmark to demonstrate the potential of this approach which allows us, for example, to examine how quantum fluctuations propagate along the ring or to test the degree of validity of the Néel-vector-tunnelling framework.

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Figure 1: Magnetic energy spectrum of Cr8 and zero-temperature INS transitions.
Figure 2: Constant-energy plots of the neutron scattering intensity for the p = 1excitation.
Figure 3: Constant-energy plots of the neutron scattering intensity for all of the possible magnetic excitations in Cr8 at 1.5 K.
Figure 4: Propagation of a local disturbance deduced from the present INS spectra and in a NVT regime.

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Acknowledgements

M.L.B. thanks the Japan Society for the Promotion of Science for a postdoctoral fellowship. We acknowledge the Institute Laue–Langevin for financial support and neutron instrument time. We thank the Institute Laue–Langevin technical staff, in particular R. Ammer who designed, machined and made alterations to the sample holders for the present experiments. T.G. thanks R. A. Ewings for the support with the HORACE package. This work was supported by the European Community through the ICT-FET Open Project MolSpinQIP, contract N. 211,284, and by the Progetti di Interesse Nazionale (PRIN) project of the Italian Ministry of Research. R. E. P. W. is supported by a Royal Society Wolfson Merit Award. S.C., G.A. and P.S. are supported by Fondazione Cariparma.

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M.L.B., T.G., S.C., J.O., H.M., H.U.G. and G.A. performed the experiment on a crystal synthesized by G.A.T. after discussion with E.J.L.M. and R.E.P.W. Data treatment was carried out by M.L.B., T.G., J.O. and H.M., and data simulations and fits were performed by M.L.B., T.G. and S.C.; S.C., G.A. and P.S. developed the idea to use four-dimensional INS measurements for a direct extraction of dynamical correlation functions of molecular nanomagnets. S.C., G.A. and P.S. also performed theoretical calculations and wrote the manuscript with input from all co-authors.

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Correspondence to Paolo Santini.

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Baker, M., Guidi, T., Carretta, S. et al. Spin dynamics of molecular nanomagnets unravelled at atomic scale by four-dimensional inelastic neutron scattering. Nature Phys 8, 906–911 (2012). https://doi.org/10.1038/nphys2431

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