Lattice dynamics contribution to the magnetic properties of molecular magnets: Raman and ultrasonic studies
Zusammenfassung der Projektergebnisse
Our main aim is to improve the understanding of magnetic scattering processes in extended and single molecular magnets as these processes are important for the coherence and dynamic properties of these systems. For this instance we investigated a large number of molecular magnets using Raman scattering, ultrasound spectroscopy and theoretical efforts. In several side lines we investigated dynamic and static effects of electron- and spin lattice coupling in coordination polymers and single molecular magnets as well as the effect of the local coordinations on the electronic states of specific transition metal ions. One of our main results is the discovery of a "phonon wipeout" and fluctuating spin state in a two-site Fe coordination polymer. Furthermore, we identified candidates for magnetic scattering in 3, 4, 5, 6, 8, 12, and 15 site single molecular magnets, as well as in giant magnetic molecules. In the latter systems multiphonon and resonance scattering up to fifth order has been identified, a quite exceptional result due to resonant intervalence charge transfer. A theoretical study used symmetry and microscopic considerations of magnetic scattering in small exchange coupled single molecule magnets. Also, the effect of local coordination and crystalline electric field (CEF) on the spin state of 3d5 metal oxygen coordination has been investigated successfully. To the end of this project we have extended our investigations on the dynamics of molecules in confinement. As confining media we used electrochemically prepared nanoporous silicon and globular proteins. We have discovered that the fluorescence dynamics of molecular magnets as well as molecular photon emitters can be modified using the interaction with the confining pore wall or molecular surrounding. Our investigations are presently continued using further ultrasonic experiments and nanoscale manipulation of molecular magnets in nonporous matrices. Some of these activities have recently been summarized in manuscripts attached to this report. The implications of these investigations are relevant for basic metrology applied to optics, i.e. enhancing the sensitivity of optical detection schemes, as well as possible schemes for optical manipulation of quantum states and single photon emitters.
Projektbezogene Publikationen (Auswahl)
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Spin state transformation of a 3d ion in the pyramidal environment and under lattice distortions, , Journal of Physics: Condensed Matter, Vol. 19. 2007, Number 15, 156216.
E. S. Zhitlukhina, K. V. Lamonova, S. M. Orel, P. Lemmens, Yu. G. Pashkevich
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Anomalous low temperature behaviour of the Co dimers in the oxo-halide CoSb2O3Br2. Journal of Solid State Chemistry, Vol. 181. 2008, Issue 10, pp. 2776-2782.
Z. Hugonin, M. Johnsson, S. Lidin, D. Wulferding, P. Lemmens, R. K. Kremer
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Microscopic Evidence of Spin-State Order and Spin State Phase Separation in Layered Cobaltites RBaCo2O5.5 with R=Y, Tb, Dy, and Ho. Physical Review Letters, Vol. 101.2008, Issue 1, 017601.
H. Luetkens, M. Stingaciu, Yu. G. Pashkevich, K. Conder, E. Pomjakushina, A. A. Gusev, K. V. Lamonova, P. Lemmens, and H.-H. Klauss,
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Anomalous frequency and intensity scaling of collective and local modes in a coupled spin tetrahedra system Cu2Te2O5Cl2. Physical Review B, Vol. 79. 2009, Issue 2, 024416.
K. Y. Choi, H. Nojiri, N. S. Dalal, H. Berger, W. Brenig, P. Lemmens
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Spectrum-sensitive phonon wipeout due to a fluctuating spin state in a Fe 2+ coordination polymer. Physical Review B, Vol. 79.2009, Issue 4, 045122.
V. Gnezdilov, P. Lemmens, P. Scheib, M. Ghosh, Yu.G. Pashkevich, H. Paulsen, V. Schünemann, J. A. Wolny, G. Agustí, J. A. Real
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A Molecular Magnet Confined in the Nanocage of a Globular Protein. ChemPhysChem, Vol. 11. 2010, Issue 2, pp. 389–393.
Samir Kumar Pal, Rajib Kumar Mitra, Pramod Kumar Verma, Dirk Wulferding, Dirk Menzel, Thom Mitra, Peter Lemmens, Achim Müller
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Manipulation of Spontaneous Emission Dynamics of Organic Dyes in the Porous Silicon Matrix. Journal of Fluorescence, Vol. 20. 2010, Issue 1, pp 283–290.
A. Makhal, S. S. Sinha, P. Kumar, P. Lemmens, S. K. Pal
