Browsing by Author "Dunstan, MA"

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    Elucidation of the electronic structure in lanthanoid-radical systems by inelastic neutron scattering
    (Australian Nuclear Science and Technology Organisation, 2021-11-24) Dunstan, MA; Calvello, S; Soncini, A; Krause-Heuer, AM; Mole, RA; Boskovic, C
    Single-molecule magnets (SMMs) are metal organic compounds which exhibit magnetic hysteresis and slow magnetic relaxation at low temperature. They have potential applications in high density data storage, quantum computing, and molecular spintronics. Coordination complexes of the trivalent lanthanoid (Ln(III)) ions are the current best performing SMMs, with examples showing hysteresis above liquid nitrogen temperature.[1] The magnetic properties of Ln(III) ions stems from the crystal field (CF) splitting of the ground Russel-Saunders state. These CF states give rise to the energy barrier to reversal of magnetisation, and can be tuned by modification of the ligand environment around the Ln(III) centre. Slow magnetic relaxation in Ln-SMMs can also be modulated by the introduction of magnetic exchange coupling with another magnetic moment, such as that of an organic radical ligand.[2] Quantifying the magnitude of magnetic exchange coupling in many Ln(III) systems is, however, difficult using conventional magnetometric techniques, due to the often large spin-orbit coupling. Inelastic neutron scattering (INS) is an ideal spectroscopic tool to measure both CF splitting and magnetic exchange coupling in Ln(III) systems.[3] We have used INS measurements to elucidate the magnetic exchange coupling and CF splitting in Ln(III)-semiquinonate complexes. Using this information we have rationalised the magnetic properties of these compounds, with the hope that a better understanding of the magnetic exchange in these systems can be used to design SMMs with improved performance. © 2021 The Authors
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    Inelastic neutron scattering of lanthanoid-radical molecular nanomagnets
    (Australian Institute of Nuclear Science and Engineering (AINSE), 2020-11-11) Dunstan, MA; Calvello, S; Krause-Heuer, AM; Soncini, A; Mole, RA; Boskovic, C
    SSingle-molecule magnets (SMMs) are materials which exhibit slow relaxation of magnetization and quantum tunneling of molecular origin. These properties make them promising for future applications in high-density data storage, as qubits in quantum computing, and in molecular spintronics.[1] The best performing SMMs are complexes of the late trivalent lanthanoid (Ln(III)) ions. The energy barrier to reversal of magnetization here stems from the crystal field (CF) splitting of the spin-orbit coupled ground state with total angular momentum J. The identity and geometry of the coordinated ligands determines the relative order, energy and composition of these CF states, such that appropriate choice of ligands can tune the CF splitting and therefore the SMM behaviour. Incorporation of organic radicals can be used to improve SMM behaviour, by shifting quantum tunneling of the magnetisation, a through-barrier relaxation pathway, from zero field.[2] The nature of magnetic exchange coupling between a Ln(III) ion and another paramagnetic moiety is, however, hard to determine, and often cannot be determined directly due to the large spin-orbit coupling inherent in many Ln compounds. Inelastic neutron scattering is a powerful experimental technique for directly measuring the CF splitting and exchange coupling in Ln(III) compounds.[3] Our group has been studying a family of compounds with formula [Ln(dbsq)Tp2], Tp– = tris(pyrazolyl)borate, dbsq– = 3,5-di-tert-butyl-semiquinonate, which show exchange coupling between the Ln(III) ion and the dbsq organic radical.[4] We have studied the INS spectra the Ln = Tb, Ho, Er, and Yb analogues on the cold neutron time-of-flight spectrometer PELICAN, as well as their magnetic properties. We observe temperature dependent CF transitions, which are compared to the energy level splitting obtained from electronic structure calculations, as well as exchange transitions in two analogues, which give us both the magnitude of and spatial information about the exchange coupling in this family of compounds.