Frontiers of Condensed Matter Physics Lecture - Title: MOLECULAR MAGNETS
Columbia: 4:10 PM EDT Pupin 329 live
Rice: 3:10 PM CDT SST 106 simulcast from Columbia U Oregon Eugene: 1:10 PM PDT simulcast from Columbia
Speaker: Prof. Myriam P. Sarachik (City College of New York)
Title: MOLECULAR MAGNETS
Abstract: Composed of a large ((~Avogadro’s) number of identical magnetic molecules of sizable spin (typically S ~
10) arranged on a regular lattice, crystals of molecular magnets are ideal laboratories for the study of nanomagnetism at the border between the classical and quantum regimes. The magnetization of these materials exhibits hysteresis below a time-scale-dependent “blocking”
temperature, exhibiting a series of steps due to the reversal of the spin magnetic moment by “macroscopic”
quantum tunneling at specific “resonant” values of the magnetic field. Focusing on Mn12-acetate as a prototypical example, and with the help of animations, we will take a quick tour of some of the fascinating physical processes that have found expression in these materials: “macroscopic”
quantum tunneling of the magnetization, Berry phase interference, an abrupt transition between thermally-assisted and ground state tunneling, and more .
A rapid reversal of the magnetic moment of the entire crystal sample often occurs in the form of a magnetic “avalanche” that proceeds as a spin-reversal front that propagates through the crystal at subsonic speed in a process that is analogous to chemical deflagration (aka chemical combustion) . Akin to a self-sustaining fire that spreads through a forest, this is a reaction-diffusion process in which the Zeeman energy released by the reversing spins as they relax toward equilibrium ignites rapid self-sustained relaxation along a deflagration front .
Recent theoretical work has identified a dipolar-driven spin-reversal process that propagates at a much faster, supersonic speed, thus magnetic “detonation” .
 "Single Molecule Nanomagnets," J. R. Friedman and M. P.
Sarachik, Ann. Rev. Cond. Matt. Phys. 1, 109 (2010).
 “Propagation of Avalanches Mn-12-acetate: Magnetic Deflagration,” Y. Suzuki, M. P. Sarachik, E. M. Chudnovsky, S. McHugh, R. Gonzales-Rubio, N. Avraham, Y. Myasoedov, E.
Zeldog, H. Shtrikman, N. E. Chaov, and G. Christou, Phys.
Rev. Lett. 95, 147201 (2005); “Magnetic Avalanches in Molecular Nanomagnets," S. McHugh and M. P. Sarachik, Mod.
Phys. Lett. B 25, 1795-1807 (2011).
 “Onset of a Propagating Self-Sustained Spin Reversal Front in a Magnetic System,” P. Subedi S. Velez, F. Macia, S. Li, M. P. Sarachik, J. Tejada, S. Mukherjee, G. Christou, and A. D. Kent, Phys. Rev. Lett. 110, 207203 (2013).
 “turbulent Fronts of Quantum Detonation in Molecular Magnets,” D. A. Garanin, Phys. Rev. B 88, 064413 (2013).
Myriam P. Sarachik (born in Antwerp, Belgium) is an American physicist and recipient of the Buckley Prize in 2005. She is a Distinguished Professor of Physics at The City College of New York since 1995 and has taught there since 1964. In 2008 she was elected to the governing council of the National Academy of Sciences. She is an experimental condensed matter physicist. Her work consists of experimenting at low temperatures. She was active in defending scientists' human rights as a member and chair of the Committee on the International Freedom of Scientists of the APS, a long-time member of the Human Rights of Scientists Committee of the New York Academy of Sciences, and a board member of the Committee of Concerned Scientists. She received her B.A. at Barnard College in 1954, her M.S. at Columbia University in 1957, and her Ph.D. at Columbia University in 1960.