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Energy Frontier Research Center Seminar

Thomas Silva- National Institute of Standards and Technology

Friday, October 20, 2017
  10:30–11 a.m.

Location: Physics Building 3035
  Parking Information

Category: Seminar


Abstract: In this talk, I will survey some recent work we have undertaken to deepen our understanding of how spin, change, and ferromagnetism interact. Our approach rests on our development of unique metrological and theoretical tools that allow us to understand these interactions on a quantitative level. I will begin by describing the theoretical work of my colleagues, Prof. Mark Hoefer and Dr. Ezio Iacocca, who have exactly recast the Landau-Lifshitz equation in terms of hydrodynamic variables, allowing for a novel interpretation of magnetization dynamics in easy-plane ferromagnets. In particular, we have examined the possibility of using a chiral Néel wall chain, which we call a dissipative exchange flow (DEF), as an efficient means of transmitting spin current over long length scales. While the transmission of spin current is still limited by the damping of the ferromagnet, the advantage of the DEF is the ability to encode the spin current magnitude in the frequency of the resultant magnetization dynamics at a fixed magnitude, as opposed to the amplitude of excitations at a fixed frequency, as is usually proposed for magnon-based logic. Next, I will describe a new method we have developed for the measurement of spin-orbit torque (SOT) in ferromagnet/nonmagnet (FM/NM) bilayers. Understanding the evolution of SOT with heavy-metal thickness in FM/NM bilayers is critical for developing magnetic memory based on SOT. However, several experiments have revealed an apparent discrepancy between damping enhancement and damping-like SOT regarding their dependence on NM thickness. Here, using linewidth and amplitude analysis of vector network analyzer ferromagnetic resonance (VNA-FMR) measurements, we simultaneously extracted damping enhancement and damping-like inverse SOT in Py/Pt bilayers, as a function of Pt thickness. By enforcing Onsager reciprocity on this data, we find that only a small fraction of angular momentum pumped out of the resonating FM is transported as spin current into the Pt. This result suggests that Pt can be an extremely useful source of SOT if the FM/NM interface can be engineered to minimize the spin loss mechanisms.

Bio: Dr. Tom Silva is Group Leader for Nanoscale Spin Dynamics at NIST in Boulder, Colorado, where he has been studying magnetization dynamics and spintronic phenomena since 1994. He obtained his undergraduate degree in Engineering Science from UC Berkeley in 1987, and Ph.D. in Engineering Physics from UCSD in 1994. His advisor was Prof. Sheldon Schultz, who subsequently became well known as a pioneer of meta-materials with his demonstration of negative refraction. For his part, Dr. Silva leads a small group that focuses on the development of novel instrumentation to quantify magnetization dynamics in a variety of systems, including nanomagnets, ferromagnet/heavy metal bilayers, and ultralow damped ferromagnet metals.

Open to: General Public
Admission: Free
Sponsor: Physics and Astronomy

Contact Information:
Physics and Astronomy
(951) 827-5033