Quantum dynamics of the Neel vector in the antiferromagnetic molecular wheel CsFe8

The inelastic neutron scattering (INS) spectrum is studied for the antiferromagnetic molecular wheel CsFe8, in the temperature range 2 - 60 K, and for transfer energies up 3.6 meV. A qualitative analysis shows that the observed peaks correspond to the transitions between the L-band states, from the ground state up to the S = 5 multiplet. For a quantitative analysis, the wheel is described by a microscopic spin Hamiltonian (SH), which includes the nearest-neighbor Heisenberg exchange interactions and uniaxial easy-axis single-ion anisotropy, characterized by the constants J and D, respectively. For a best-fit determination of J and D, the L band is modeled by an effective SH, and the effective SH concept extended such as to facilitate an accurate calculation of INS scattering intensities, overcoming difficulties with the dimension of the Hilbert space. The low-energy magnetism in CsFe8 is excellently described by the generic SH used. The two lowest states are characterized by a tunneling of the Neel vector, as found previously, while the higher-lying states are well described as rotational modes of the Neel vector.Comment: 12 pages, 10 figures, REVTEX4, to appear in PR

Magnetic relaxation studies on a single-molecule magnet by time-resolved inelastic neutron scattering

Time-resolved inelastic neutron scattering measurements on an array of single-crystals of the single-molecule magnet Mn12ac are presented. The data facilitate a spectroscopic investigation of the slow relaxation of the magnetization in this compound in the time domain.Comment: 3 pages, 4 figures, REVTEX4, to appear in Appl. Phys. Lett., for an animation see also http://www.dcb.unibe.ch/groups/guedel/members/ow2/trins.ht

Postsynthesis stabilization of free-standing mesoporous silica films

Mixed ammonia-water vapor postsynthesis treatment provides a simple and convenient method for stabilizing mesostructured silica films. X-ray diffraction, transmission electron microscopy, nitrogen adsorption/desorption, and solid-state NMR (C-13, Si-29) were applied to study the effects of mixed ammonia-water vapor at 90 degreesC on the mesostructure of the films. An increased cross-linking of the silica network was observed. Subsequent calcination of the silica films was seen to cause a bimodal pore-size distribution, with an accompanying increase in the volume and surface area ratios of the primary (d = 3 nm) to secondary (d = 5-30 nm) pores. Additionally, mixed ammonia-water treatment was observed to cause a narrowing of the primary pore-size distribution. These findings have implications for thin film based applications and devices, such as sensors, membranes, or surfaces for heterogeneous catalysis

Quantized antiferromagnetic spin waves in the molecular Heisenberg ring CsFe8

We report on inelastic neutron scattering (INS) measurements on the molecular spin ring CsFe$_8$, in which eight spin-5/2 Fe(III) ions are coupled by nearest-neighbor antiferromagnetic Heisenberg interaction. We have recorded INS data on a non-deuterated powder sample up to high energies at the time-of-flight spectrometers FOCUS at PSI and MARI at ISIS, which clearly show the excitation of spin waves in the ring. Due to the small number of spin sites, the spin-wave dispersion relation is not continuous but quantized. Furthermore, the system exhibits a gap between the ground state and the first excited state. We have modeled our data using exact diagonalization of a Heisenberg-exchange Hamiltonian together with a small single-ion anisotropy term. Due to the molecule's symmetry, only two parameters $J$ and $D$ are needed to obtain excellent agreement with the data. The results can be well described within the framework of the rotational-band model as well as antiferromagnetic spin-wave theories.Comment: 10 pages, 9 figures, REVTEX

INTERMED - an alternative to the psychosocial evaluation of transplant patients ? Results of a prospective study

Fragestellung: Bislang liegen zwei standardisierte Interviews zur Evaluierung der psychosozialen Situation von TX-Patienten vor: das Psychosocial Assessment of Candidates for Transplantation (PACT) und die Transplant Evaluation Rating Scale (TERS). Das Ziel der laufenden, multizentrischen Studie ist zu eruieren, ob sich 1. das halbstrukturierte Interview- und Ratingverfahren der biopsychosozialen Belastung und Versorgungsnotwendigkeit INTERMED (HUYSE et al., 2001) zur psychosozialen Evaluierung während der TX-Vorbereitung eignet, und 2. ob das INTERMED (IM) eine Vorhersage der Lebensqualität nach der TX ermöglicht. Methoden: 120 konsekutive Organ-TX-Kandidaten wurden während ihrer Wartezeit mit IM, TERS, SF-36 und HADS evaluiert. Die Konvergenzvalidität des IM mit den vergleichbaren klinischen Instrumenten wurde mittels Korrelationsanalysen, der Einfluss der vor der TX erhobenen Baseline-Variablen auf die abhängige Variable Körperliche Lebensqualität (SF-36) mittels linearen Regressionsanalysen untersucht. Ergebnisse: 73 Nieren-, 20 Leber- und 25 Herz-TX-Kandidaten wurden vor und bisher 30 Patienten 1 Jahr nach der TX untersucht. Die Konvergenz des IM mit der TERS (r ,524) und dem SF-36 (Körp. LQ r -,324; Psych. LQ r -,234) und HADS (r ,384) ist mittelgradig bis hoch. Das beste Prädiktormodell für die Körp. LQ (R2 ,72) der Patienten 1 Jahr nach der TX besteht aus den Merkmalen Alter (β -,52), Organ: Leber (β 12,9) und dem IM-Summenwert (β 1,25). Diskussion: Die konvergente und prädiktive Validität des IM für die Anwendung bei TX-Patienten konnten wir nachweisen. Gegenüber den anderen Instrumenten bietet das IM zusätzliche Vorteile für die klinische Praxis: neben Belastungen der Patienten werden auch soziale Integration und Versorgungsbedarf eingeschätzt bzw. kann direkt in weiterführende diagnost. und therapeut. Maßnahmen übergeleitet werden. Das IM bietet sich an, die gesundheitliche Entwicklung eines TX-Patienten abzuschätzen und präventive Maßnahmen zu treffen

Low-temperature single-crystal Raman and neutron-diffraction study of the hydrogenous ammonium copper(II) tutton salt and the deuterated analogue in the metastable state

Low-temperature (15 K) single-crystal neutron-diffraction structures and Raman spectra of the salts (NX4)(2)[CU(OX2)(6)](SO4)(2), where X = H or D, are reported. This study is concerned with the origin of the structural phase change that is known to occur upon deuteration. Data for the deuterated salt were measured in the metastable state, achieved by application of 500 bar of hydrostatic pressure at similar to303 K followed by cooling to 281 K and the subsequent release of pressure. This allows for the direct comparison between the hydrogenous and deuterated salts, in the same modification, at ambient pressure and low temperature. The Raman spectra provide no intimation of any significant change in the intermolecular bonding. Furthermore, structural differences are few, the largest being for the long Cu-O bond, which is 2.2834(5) and 2.2802(4) Angstrom for the hydrogenous and the deuterated salts, respectively. Calorimetric data for the deuterated salt are also presented, providing an estimate of 0.17(2) kJ/mol for the enthalpy difference between the two structural forms at 295.8(5) K. The structural data suggest that substitution of hydrogen for deuterium gives rise to changes in the hydrogen-bonding interactions that result in a slightly reduced force field about the copper(II) center. The small structural differences suggest different relative stabilities for the hydrogenous and deuterated salts, which may be sufficient to stabilize the hydrogenous salt in the anomalous structural form