Colorado State University
Friday, August 9, 2019
A fractal is a shape made of parts each of which is similar to the whole in some way. One can group fractals into two main categories, (i) exact fractals in which the same feature replicates itself on successively smaller scales and (ii) statistical fractals that display statistically similar features. Statistical fractals have been observed in a wide variety of physical systems, ranging from material structures to stock price fluctuations. In contrast, exact fractals are relatively rare in nature, though they can be very easily constructed by mathematical models. This presentation will report on the experimental observation of exact fractals in nonlinear spin waves in magnetic materials. There will be two parts. Part I will be on soliton fractals in a feedback ring that consists of (1) a long and narrow magnetic Y3Fe5O12 (YIG) thin film strip that supports spin waves and (2) an amplifier that amplifies the output signal from the YIG strip and then fed it back to the input of the strip.1 Part II will be on spin-wave fractals in a quasi-1D magnonic crystal that consists of a YIG film strip with periodic transversal lines etched into the film.2
 “Observation of spin wave soliton fractals in magnetic film active feedback rings,” Mingzhong Wu, Boris A. Kalinikos, Lincoln D. Carr, and Carl E. Patton, Phys. Rev. Lett. 96, 187202 (2006).
 “Spontaneous exact spin-wave fractals in magnonic crystals,” Daniel Richardson, Boris A. Kalinikos, Lincoln D. Carr, and Mingzhong Wu, Phys. Rev. Lett. 121, 107204 (2018).
Note: If time permits, the speaker will also present a very recent paper on “Spin-Orbit Torque-Induced Magnetization Reversal in Topological Insulator/Magnetic Insulator Bi-Layered Structures;” this paper has been accepted for publication by Science Advances recently.