Faculty: Hoatson , Kossler , Manos, Reilly

NMR investigations cover a broad range of systems including single crystals, high-temperature superconductors, polycrystalline molecular crystals, inclusion compounds, metals, amorphous alloys and glassy polymers, and thermotropic liquid crystals. The coherent theme in these studies is to understand how the local environment modifies and constrains molecular order as well as rotational, librational, and translational dynamics. By a judicious choice of systems, it is possible to focus attention on specific constraints imposed by inter- and intra-molecular forces. This provides an exciting opportunity to improve our understanding of the connections between dynamics at the molecular level and macroscopic properties of technologically interesting materials.

Deuteron nuclear magnetic resonance spectroscopy (2H-NMR) is capable of probing motion over a very wide kinetic range (10*-1 - 10*12 s-1). Novel pulse sequences for determining spin relaxation times have been developed and are being used to determine the static and dynamic behavior in solids. The new techniques are essentialfor studies of motion of both host and guest molecules in inclusion compounds. Molecular dynamic simulations are now capable of dealing with time scales relevant to spin relaxation processes. This provides an important synergism between simulations and experiment: agreement between NMR data and computer simulations can help check the model potential functions, and direct calculation of the correlation functions obviates the dependence on simple models for interpreting the experimental data.

Installed in May, 2005, the high field NMR laboratory at William and Mary houses three spectrometers. The flagship instrument is a Bruker Biospin, Inc., 17.6T (750 MHz) spectrometer. First of its kind in the Commonwealth of Virginia, this spectrometer is used primarily for multinuclear NMR investigations of solid state structure and dynamics. The high field spectrometer features an assortment of triple resonance magic angle spinning probes, cabable of operating between -150C and 150C, with spinning speeds up to 35 kHz. The laboratory also houses 7.05T and 4.7T spectrometers designed for solid state NMR studies. For pictures of the high field spectrometer installation and comissioning, click here.

High resolution 13C NMR spectra are being obtained with cross polarization, magic angle spinning, and high-power proton decoupling (CPMAS). A new two-dimensional NMR technique, Variable Angle Correlation Spectroscopy (VACSY), has recently been implemented. This two-dimensional experiment yields 13C spectra in which one dimension resolves isotropic chemical shifts, while the second dimension gives the corresponding shielding anisotropies. VACSY has promising applications for structural and dynamic studies of small molecular crystals, inclusion compounds, and high-performance thermoplastic polymers.

Studies of dilute solutions of hydrogen in niobium are directed at the precipitation process and hydride phase formation. The phase separation can be studied by 1H NMR techniques. This topic is of particular interest because hydrogen is a common impurity and can impair the quality factor of superconducting niobium cavities. A research program involving high temperature superconductors is focused on their behavior at microwave frequencies. For polycrystalline films, grain boundaries act as weak links (or Josephson junctions); thus the grain structure and the external field are very important. Shielding behavior and trapped flux are also subjects of study.

A more detailed description of the group can be found here.

The field of muon spin rotation/relaxation/resonance in (muSR) solids has generated a great deal of excitement over the past ten years. As the simplest charged probe, the muon aids in the study of many of the fundamental problems in solid state physics. The first experiments, measuring the hyperfine fields of muons in ferromagnetic materials were performed here in 1972. Subsequently the technique has been used to investigate the internal magnetic fields in spin glasses, ferro and antiferromagnets, and superconductors. Attention has also been given to the behavior of the muon in the solid, in particular the muon's site, diffusion characteristics and trappings. Currently, experiments are in progress on hydrides, heavy fermion superconductors and magnetic compounds, using this group's stopped muon channel at (BNL. Most recently we have measured the penetration depths for some of the new high temperature superconductors. Internal magnetic field distributions have been seen even when there have been no applied fields e.g. in the heavy fermion system CeCu2.1Si2.