High-Field Electron Paramagnetic Resonance and Molecular Nanomagnetism Research at the National High Magnetic Field Laboratory
Dr. Stephen Hill
Department of Physics
Florida State University
Wednesday, May 7, 2014
C2-361 (Reading Room)
Abstract: Most Electron Paramagnetic Resonance (EPR) research is performed at the X-Band frequency of 9.5 GHz. More specialized commercial instruments exist operating at K-Band (25 GHz), Q-Band (35 GHz) and W-Band (95 GHz). The EPR facilities at the US National High Magnetic Field Laboratory (NHMFL) in Tallahassee, FL, offer scientists from all over the world opportunities to use several home-built, high-field/high-frequency instruments with continuous coverage from ~10 GHz to 1 THz . Magnets are also available providing magnetic fields of up to 45 T — roughly one million times stronger than the earth’s magnetic field. EPR performed at these extremes offers tremendous advantages for certain problems spanning diverse research fields from condensed matter physics, to chemistry, to biology. After a brief overview of the kinds of research conducted by EPR users at the NHMFL, the remainder of the talk will focus on molecular nanomagnets ¾ molecules that contain either a single magnetic ion, or multiple exchange-coupled magnetic ions that possess a well defined collective magnetic moment (spin) at low temperatures. These molecules are of interest in terms of their potential future use as memory elements in both classical and quantum logic devices. From a fundamental point-of-view, they also form high-quality bulk crystals in which every molecule has the same spin, orientation, magnetic anisotropy, etc., enabling detailed spectroscopies of large ensembles of nominally independent nanomagnets that have so far been lacking for other types of magnetic nanostructures. Such studies have thus provided crucial insights into the quantum nature of magnetization dynamics at the nanoscale. This talk will highlight results obtained using high-frequency/high-field EPR , emphasizing some of the discoveries that have contributed to a recent shift away from the study of large multinuclear clusters to simpler molecules containing highly anisotropic magnetic ions such as lanthanides or transition metals with unquenched orbital moments.
 J. Liu, E. del Barco, S. Hill, in Molecular Magnets – Physics and Applications, pp 77-110, eds. J. Bartolomé, F. Luis, J. F. Fernández, Springer Series on NanoScience and Technology (Springer-Verlag, Berlin-Heidelberg 2014) ); also http://xxx.lanl.gov/abs/1302.7305.