High-Frequency Electron-Spin-Resonance Study of the Octanuclear Ferric Wheel CsFe8_8

High-frequency ($f$ = 190 GHz) electron paramagnetic resonance (EPR) at magnetic fields up to 12 T as well as Q-band ($f$ = 34.1 GHz) EPR were performed on single crystals of the molecular wheel CsFe$_8$. In this molecule, eight Fe(III) ions, which are coupled by nearest-neighbor antiferromagnetic (AF) Heisenberg exchange interactions, form a nearly perfect ring. The angle-dependent EPR data allow for the accurate determination of the spin Hamiltonian parameters of the lowest spin multiplets with $S \leq$ 4. Furthermore, the data can well be reproduced by a dimer model with a uniaxial anisotropy term, with only two free parameters $J$ and $D$. A fit to the dimer model yields $J$ = -15(2) cm$^{-1}$ and $D$ = -0.3940(8) cm$^{-1}$. A rhombic anisotropy term is found to be negligibly small, $E$ = 0.000(2) cm$^{-1}$. The results are in excellent agreement with previous inelastic neutron scattering (INS) and high-field torque measurements. They confirm that the CsFe$_8$ molecule is an excellent experimental model of an AF Heisenberg ring. These findings are also important within the scope of further investigations on this molecule such as the exploration of recently observed magnetoelastic instabilities.Comment: 21 pages, 8 figures, accepted for publication in Inorganic Chemistr

Molecular lanthanide single-ion magnets: from bulk to submonolayers

Single-ion magnets (SIMs) are mononuclear molecular complexes exhibiting slow relaxation of magnetization. They are currently attracting a lot of interest because of potential applications in spintronics and quantum information processing. However, exploiting SIMs in, e.g. molecule-inorganic hybrid devices requires a fundamental understanding of the effects of molecule-substrate interactions on the SIM magnetic properties. In this review the properties of lanthanide SIMs in the bulk crystalline phase and deposited on surfaces in the (sub) monolayer regime are discussed. As a starting point trivalent lanthanide ions in a ligand field will be described, and the challenges in characterizing the ligand field are illustrated with a focus on several spectroscopic techniques which are able to give direct information on the ligand-field split energy levels. Moreover, the dominant mechanisms of magnetization relaxation in the bulk phase are discussed followed by an overview of SIMs relevant for surface deposition. Further, a short introduction will be given on x-ray absorption spectroscopy, x-ray magnetic circular dichroism and scanning tunneling microscopy. Finally, the recent experiments on surface-deposited SIMs will be reviewed, along with a discussion of future perspectives

The Flip Side: An Investigation into the Depersonalization of Communication

The author investigated the depersonalization of student communication in grades six through twelve. The Flip Side Survey was run to focus in on whether or not the use of instant message programs and text messages via cellular telephones is depersonalizing communication between 6th through 12th grade students (N=213). Depersonalization was broken down in to five constructs: empathy, compassion, conversational cue usage, personal communication skills, and consequence recognition. Each construct was measured in relationship to face-to-face communication and each question was repeated in relationship to text message and instant message communication. The results showed little evidence to support the depersonalization of communication due to the use of text/instant messaging

Voltage-controlled electron-hole interaction in a single quantum dot

The ground state of neutral and negatively charged excitons confined to a single self-assembled InGaAs quantum dot is probed in a direct absorption experiment by high resolution laser spectroscopy. We show how the anisotropic electron-hole exchange interaction depends on the exciton charge and demonstrate how the interaction can be switched on and off with a small dc voltage. Furthermore, we report polarization sensitive analysis of the excitonic interband transition in a single quantum dot as a function of charge with and without magnetic field.Comment: Conference Proceedings, Physics and Applications of Spin-Related Phenomena in Semiconductors, Santa Barbara (CA), 2004. 4 pages, 4 figures; content as publishe

The Sgraffito and Champlevé Ceramics from Ḫirbat al-Minya at the Sea of Galilee

Die vorliegende Magisterarbeit ist eine Auswertung der glasierten Keramikfunde vom Typ der Sgraffito- und Champlevé-Waren aus Ḫirbat al-Minya am See Genezareth dar. Die kastellartige Anlage von Ḫirbat al-Minya zählt zum Typus der sogenannten Wüstenschlösser, einer Gruppe ländlicher Residenzen, die unter den Umayyaden im 7. bis 8. Jahrhundert in Syrien und Palästina entstanden sind. Bei den Ausgrabungen durch deutsche Archäologen in den 1930er Jahren wurden große Mengen an Keramik geborgen, von denen ein Teil, zusammen mit weiteren Kleinfunden, in das Berliner Museum für Islamische Kunst gelangten, wo sie jedoch nicht mehr einer abschließenden Grabungsauswertung unterzogen werden konnten. Dabei deuten besonders die Funde an glasierter Keramik auf eine Besiedlung von Ḫirbat al-Minya auch in nachummayyadischer Zeit hin. Die vorliegende Auswertung des Berliner Bestandes an Sgraffito und Champlevé-Ware, die neben schlickerbemalter Ware den Großteil am glasierten Keramik-Korpus ausmacht, ermöglicht somit einerseits Rückschlüsse auf eine relativ chronologische mittelalterliche Besiedlung von Ḫirbat al-Minya. Andererseits wird durch die Auswertung eine Vergleichsbasis für andere Fundorte im Großraum Syrien (Bilād aš-Šām) vorgelegt, wo die Auswertung glasierter Gebrauchskeramik gegenüber den sogenannten Luxuswaren lange Zeit vernachlässigt wurde.The thesis presents the glazed ceramic findings of the Sgraffito and Champlevé type from the ruin Ḫirbat al-Minya at the Sea of Galilee in present-day Israel. The ruin belongs to a number of rural residences built under the Islamic dynasty of the Umayyads in Syria and Palestine, the so-called 'desert castles'. During the excavations carried out by German archaeologists in the 1930s vast amounts of ceramics were found, of which a considerable part together with other small finds was given to the Berlin Museum for Islamic Art. However, no final evaluation of the excavations could then be undertaken. The finds of glazed ceramics particularly suggest that Ḫirbat al-Minya was still populated in medieval times in the aftermath of the Ummayyad dynasty. The present analysis of the Berlin corpus of glazed Sgraffito and Champlevé ceramics, which together with slip-painted wares forms the bulk of glazed ceramics found, makes it possible to draw conclusions for a relative dating of the medieval settlement at Ḫirbat al-Minya. Furthermore, the analysis forms a point of comparative reference for other find spots in Greater Syria (Bilād aš-Šām), where the analysis of glazed domestic wares has been much neglected in favour of so-called luxury wares