Highpressure Magnetism Studied With Nuclear Resonant Spectroscopy
by
W. Sturhahn, Argonne National Laboratory
→
Europe/Berlin
Bldg. 25b, Room 109
Bldg. 25b, Room 109
Description
The development of nuclear resonant scattering techniques at third generation synchrotron radiation facilities around the world has been very successful over the last decade. New and exciting opportunities for the study of vibrational and magnetic properties of condensed matter have opened up for research areas like biophysics, geophysics, and nanoscience. In particular, the determination of the vibrational density of states with nuclear resonant inelastic xray scattering (NRIXS) and the study of valences and magnetic properties with synchrotron Mössbauer spectroscopy (SMS) produced unique results. In this contribution, we discuss the application of nuclear resonant spectroscopy to magnetic materials under extremely high pressures. We show that SMS is a powerful tool to investigate magnetic ordering as well as localized 3delectron configurations in Fe. Pressure dependent magnetic ordering transitions in Fe2O3, Fe3S, and Fe3C are described. The more or less sudden change of the 3delectron configuration of Fe in planetary materials such as (Fe,Mg)O periclase is discussed intensely in the geoscience sector. These so called “spin transitions” or “spin crossovers” may be soughtafter causes for various effects and have significant implications for the understanding of Earth's lower mantle processes. Here we describe the analysis of spin crossovers using SMS and NRIXS. In conjunction with magnetic ordering or spin crossovers, the vibrational properties of the material can change dramatically. We demonstrate this connection with pressure dependent NRIXS studies on the materials mentioned above and provide views into the possible implications for Earth sciences. Nuclear resonant spectroscopy studies require a suitable isotope. Clearly 57Fe has spawned the largest interest so far, but we also review the selection of other nuclear resonances for magnetism studies. A significant scientific impact is expected to result from increased brilliance and flux resulting from planned upgrades, for example at the Advanced Photon Source (APS). With the implementation of an APS storage ring upgrade including extended straight sections, optimized undulators, and 200 mA operation current, a gain of about a factor of ten in spectral flux in the 14 keV to 30 keV range can be expected. For inelastic xray spectroscopy, this upgrade would enable a significant improvement of the energy resolution from 12 meV now to 0.1 meV. We will briefly discuss such a capability which would be an important step to explore new dynamical aspects of biological molecules and proteins, magnetic nanostructures, and materials in planetary interiors. This work is supported by the U. S. Department of Energy, Office of Science, Office of Basic Energy Sciences, under Contract No. DEAC0206CH11357.
