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Physics Event · · ·

Hudspeth Memorial Lecture: Prof. Myriam Sarachik, City University of New York

Date and Time: Wednesday, September 18, 2013 at 4:15 PM (CDT)
Location: RLM 4.102

Hudspeth Memorial Lecture

Prof. Myriam Sarachik, City University of New York

"Quantum Tunneling and Magnetic Deflagration"

4:15pm, The John A. Wheeler Lecture Hall (RLM 4.102)

Coffee and cookies will be served at 4:00pm in RLM 4.102

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 nano-magnetism at the border between the classical and quantum regimes. Using Mn12-acetate as a prototypical example, and with the help of animations, we will take a quick tour of some 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…… The magnetization exhibits hysteresis at low temperatures in response to a magnetic field applied along the crystal easy axis, exhibiting a series of steps due to the reversal of the spin magnetic moment by quantum tunneling at specific “resonant” values of the magnetic field. An abrupt reversal of the magnetic moment of the entire sample can occur instead in the form of a magnetic avalanche in a process that is analogous to chemical deflagration (aka chemical combustion). In sufficiently high bias field, the Zeeman energy released by the reversing spins as they relax toward equilibrium leads to a dynamical instability that ignites rapid self-sustained relaxation along a deflagration front that propagates throughout the crystal at a constant subsonic speed. Recent experiments will be shown in which a trigger heat pulse and transverse and longitudinal magnetic fields were used to study and control the crossover between thermally driven magnetic relaxation and self-sustained magnetic deflagration, akin to a self-sustaining fire that spreads through the forest.

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