Spin-Wave Theory and its Applications to Neutron Scattering and THz Spectroscopy

Two of the most powerful tools used to study magnetic materials are inelastic neutron scattering and THz spectroscopy. Because the measured spectra provide a dynamical fingerprint of a magnetic material, those tools enable scientists to unravel the structure of complex magnetic states and to determine the microcscopic interactions that produce them. This book discusses the experimental techniques of inleastic neutron scattering and THz spectroscopy and provides the theoretical tools required to analyze their measurements using spin-wave theory. For most materials, this analysis can resolve the microscopic magnetic interactions such as exchange, anisotropy, and Dzyaloshinskii-Moriya interactions. Assuming a background in elementary statistical mechanics and a familiarity with the quantized harmonic oscillator, this book presents a comprehensive review of spin-wave theory and its applications to both inelastic neutron scattering and THz spectroscopy. Spin-wave theory is used to study several model magnetic systems, including non-collinear magnets such as spirals and cycloids that are produced by geometric frustration, competing exchange interactions, or Dzyaloshinskii-Moriya interactions. Several case studies utilizing spin-wave theory to analyze inelastic neutron-scattering and THz spectroscopy measurements are presented. These include both single crystals and powders and both oxides and molecule-based magnets. In addition to sketching the numerical techniques used to fit dynamical spectra based on microscopic models, this book also contains over 70 exercises that can be performed by beginning graduate students.

Randy Fishman received his Ph.D. in physics from Princeton University in 1985. He became a faculty member at North Dakota State University in 1989 and arrived at Oak Ridge National Laboratory as a staff scientist in 1995. He was a former leader of the Materials Theory group and is currently a Distinguished R&D Staff scientist at ORNL. As a condensed-matter theorist, he studies the complex magnetic states of oxides and molecule based magnets. Fishman is the author of over 160 scientific publications.

Dr. Jaime Fernandez-Baca received a BSc in Physics at the Universidad Nacional de Ingenieria. He joined the Peruvian Institute of Nuclear Energy, where he was awarded the International Atomic Energy Agency (IAEA) fellowship. He received his Ph.D in Physics at the University of Maryland College Park in 1986. Currently he is a Distinguished Research Staff member in ORNL's Quantum Condensed Matter Division, and the Leader of the Triple Axis Spectroscopy group at the High Flux Isotope Reactor.

Toomas Rõõm received a PhD in physics from Tartu University in 1993. He has been affiliated with National Institute of Chemical Physics and Biophysics in Tallinn, Estonia since 1984 where he is a research professor currently. He has been post-doc at the University of California, Berkeley and at McMaster University, Hamilton, Ontario, Canada. Together with his colleague Dr. U. Nagel, he received a state award for Interaction of terahertz radiation with materials in 2016.