Nuclear Magnetic Resonance

The NMR technique is a powerful spectroscopic technique which probes the local magnetic and electronic properties of materials. It is complementary to neutron and optical spectroscopy, and enables the investigation of local hyperfine interactions, fluctuations and excitations. The NMR laboratory at Ames has a wide array of spectrometers and magnets making the lab one of the best equipped. It also has gained an international reputation in the many years of its operation. The presence of a strong solid state NMR facility in Ames has been very effective for investigating on site and in a timely fashion the microscopic properties of new materials and phases prepared and characterized by other local researchers giving Ames Lab a distinct advantage.

People and Collaborators

Main external collaborators:
Alessandro Lascialfari, Dept. of Physics, University of Pavia, Italy
Y. Furukawa, Division of Physics, Hokkaido University, Sapporo, Japan
B.J. Suh, Dept. of Physics, The Catholic University of Korea, Puchon, Korea Zeehoon Jang, Seoul, Korea
Andrea Cornia, M. Affronte, Dept. of Chemistry, University of Modena, Italy
Dante Gatteschi, Andrea Caneschi, Roberta Sessoli, Dept. of Chemistry, University of Florence, Italy

 Inelastic neutron scattering (INS) is a very useful tool for the study of magnetic molecules since this technique can provide quantitative information regarding the characteristics of the spectrum of discrete magnetic energy levels as well as information on the matrix elements for transitions. Thus, the temperature and magnetic field dependence of the INS spectra and their intensities can provide critical tests of theoretical predictions. This technique complements other experimental methods in our group and together they provide valuable information about the magnetic properties of magnetic molecules. Our neutron scattering experiments have been conducted on a variety of spectrometers in the US and in Europe, including the Disc-Chopper Spectrometer at NIST and on the OSIRIS at ISIS (UK). With the upcoming commissioning of the Spallation Neutron Source (SNS) we eagerly look forward to new capabilities that are crucial to our studies, including new spectrometers with improved energy resolution, neutron intensities and energy ranges that were heretofore unavailable. All samples (regular and deuterated) are synthesized at Ames Laboratory.

People and Collaborators

Main external collaborators:
Bella Lake and D. Tennant, Hahn-Meitner Institute, Berlin, Germany
Stephen E. Nagler, Solid State Division, Oak Ridge National Laboratory, Oak Ridge, TN
Yiming Qiu, National Institute of Standards and Technology, Gaithersburg, MD

 Of key importance in characterizing the magnetic properties of magnetic molecules is the availability of data for magnetization versus temperature and magnetic field. While SQUID magnetometers typically provide magnetization data for temperatures above 2 K and magnetic fields up to 7 T, in many instances it is important to be able to reach millikelvin temperatures and fields in excess of 15 T. These demanding requirements are necessary so as to compare with quantitative predictions of theoretical models of magnetic molecules as well as to complement other types of measurements, for example inelastic neutron scattering that are performed in the wider range of temperature and magnetic field. This level of experimental capability has been initiated starting in 2006 and will continue in full force during 2007, allowing measurements with an equipment base temperature of 10 mK and fields up to 16 T with a currently developed cantilever-based DC magnetometer. In addition to magnetization measurements, our laboratory will in the near future provide AC susceptibility and specific heat data. In the millikelvin regime the specific heat data provides useful information concerning the magnetic excitations in magnetic molecules since phonon contributions are negligible.
The facility was established recently (summer 2005) to address this need for advanced characterization of novel materials. The experimental capabilities include unique tunnel-diode resonator technique (six orders of magnitude more sensitive than commercial SQUID) as well as magneto-optical visualization of magnetic fields in superconductors and ferromagnets. A just-installed versatile dilution refrigerator system extends temperatures down to 10 mK and magnetic fields to 16 Tesla. The upper temperature range approaches 1000 K. During next three years it is planned to complete the infrastructure and measurement capabilities of the laboratory and be fully engaged in several research projects. Experimentally, the major effort will be devoted to building advanced measurement capabilities on a dilution refrigerator as well as extending operation of the unique tunnel-diode oscillator to lower and higher temperatures, variable frequency, pressure as well as measurements of dielectric constants and multiferroics

People and Collaborators