Spin dynamics in the single-ion magnet [Er(W5O18)2]9−

In this work we present a detailed NMR and \u3bc+SR investigation of the spin dynamics in the new hydrated sodium salt containing the single-ion magnet [Er(W5O18)2]9-. The H1NMR absorption spectra at various applied magnetic fields present a line broadening on decreasing temperature which indicates a progressive spin freezing of the single-molecule magnetic moments. The onset of quasistatic local magnetic fields, due to spin freezing, is observed also in the muon relaxation curves at low temperature. Both techniques yield a local field distribution of the order of 0.1-0.2 T, which appears to be of dipolar origin. On decreasing the temperature, a gradual loss of the H1NMR signal intensity is observed, a phenomenon known as wipe-out effect. The effect is analyzed quantitatively on the basis of a simple model which relies on the enhancement of the NMR spin-spin, T2-1, relaxation rate due to the slowing down of the magnetic fluctuations. Measurements of spin-lattice relaxation rate T1-1 for H1NMR and of the muon longitudinal relaxation rate \u3bb show an increase as the temperature is lowered. However, while for the NMR case the signal is lost before reaching the very slow fluctuation region, the muon spin-lattice relaxation \u3bb can be followed until very low temperatures and the characteristic maximum, reached when the electronic spin fluctuation frequency becomes of the order of the muon Larmor frequency, can be observed. At high temperatures, the data can be well reproduced with a simple model based on a single correlation time \u3c4=\u3c40exp(\u394/T) for the magnetic fluctuations. However, to fit the relaxation data for both NMR and \u3bc+SR over the whole temperature and magnetic field range, one has to use a more detailed model that takes into account spin-phonon transitions among the Er3+ magnetic sublevels. A good agreement for both proton NMR and \u3bc+SR relaxation is obtained, which confirms the validity of the energy level scheme previously calculated from an effective crystal field Hamiltonian

Structure and Dynamics in Polyacrylami de Hydrogels With and Without Probe Particles : A Light Scattering Study

この論文は国立情報学研究所の電子図書館事業により電子化されました。研究会報

Dynamics of Deinococcus radiodurans under Controlled Growth Conditions

Deinococcus radiodurans is a potent radiation resistant bacterium with immense potential in nuclear waste treatment. In this investigation, the translational and rotational dynamics of dilute suspensions of D. radiodurans cultured under controlled growth conditions was studied by the polarized and depolarized dynamic light-scattering (DLS) techniques. Additionally, confocal laser scanning microscopy was used for characterizing the cultured samples and also for identification of D. radiodurans dimer, tetramer, and multimer morphologies. The data obtained showed translational diffusion coefficients (D(T)) of 1.2 × 10(−9), 1.97 × 10(−9), and 2.12 × 10(−9) cm(2) /s, corresponding to an average size of 3.61, 2.22, and 2.06 μm, respectively, for live multimer, tetramer, and dimer forms of D. radiodurans. Depolarized DLS experiments showed very slow rotational diffusion coefficients (D(R)) of 0.182/s for dimer and 0.098/s for tetramer morphologies. No measurable rotational diffusion was observed for multimer form. Polarized DLS measurements on live D. radiodurans confirmed that the bacterium is nonmotile in nature. The dynamics of the dead dimer and tetramer D. radiodurans were also studied using polarized and depolarized DLS experiments and compared with the dynamics of live species. The dead cells were slightly smaller in size when compared to the live cells. However, no additional information could be obtained for dead cells from the polarized and depolarized dynamic light-scattering studies