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Register a new userQuantum spin coherence in halogen-modified Cr$_7$Ni molecular nanomagnets
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Among the factors determining the quantum coherence of the spin in molecular magnets is the presence and the nature of nuclear spins in the molecule. We have explored modifying the nuclear spin environment in Cr$_7$Ni-based molecular nanomagnets by replacing hydrogen atoms with deuterium or the halogen atoms, fluorine or chlorine. We find that the spin coherence, studied at low temperatures by pulsed electron spin resonance, is modified by a range of factors, including nuclear spin and magnetic moment, changes in dynamics owing to nuclear mass, and molecular morphology changes.
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We study the magnetization and the spin dynamics of the Cr$_7$Ni ring-shaped magnetic cluster. Measurements of the magnetization at high pulsed fields and low temperature are compared to calculations and show that the spin Hamiltonian approach provides a good description of Cr$_7$Ni magnetic molecule. In addition, the phonon-induced relaxation dynamics of molecular observables has been investigated. By assuming the spin-phonon coupling to take place through the modulation of the local crystal fields, it is possible to evaluate the decay of fluctuations of two generic molecular observables. The nuclear spin-lattice relaxation rate $1/T_1$ directly probes such fluctuations, and allows to determine the magnetoelastic coupling strength.
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I. S. Tupitsyn Pacific Institute for Theoretical Physics
, n University of British Columbia
2004
The spin coherence phenomena and the possibility of their observation in nanomagnetic insulators attract more and more attention in the last several years. Recently it has been shown that in these systems in large transverse magnetic field there can be a fairly narrow coherence window for phonon and nuclear spin-mediated decoherence. What kind of spin dynamics can then be expected in this window in a crystal of magnetic nanomolecules coupled to phonons, to nuclear spin bath and it to each other via dipole-dipole interactions? Studying multispin correlations, we determine the region of parameters where coherent clusters of collective spin excitations can appear. Although two particular systems, namely crystals of $Fe_8$-triazacyclonane and $Mn_{12}$-acetate molecules, are used in this work to illustrate the results, here we are not trying to predict an existence of collective coherent dynamics in some particular system. Instead, we discuss the way how any crystalline system of dipole-dipole coupled nanomolecules can be analyzed to decide whether this system is suitable for attempts to observe coherent dynamics. The presented analysis can be useful in the search for magnetic systems showing the spin coherence phenomena.
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