Publications by John Gregg

Onset of spin wave time-domain fractals in a dynamic artificial crystal

Journal of Magnetism and Magnetic Materials Elsevier 495 (2019) 165868

A Inglis, J Gregg

<p>We report on the first observation of an exact fractal pattern in the time-domain arising spontaneously from adynamic artificial crystal (DAC). The all-magnon process occurs in a passive, unlithographed magnetic wave-guide. The DAC was created by a standing spin wave of frequency ƒ<sub>DAC</sub> in a region of nonlinear waveguide, resulting in a spatio-temporally periodic potential. The interaction of travelling spin waves of frequency ƒ′ with the DAC resulted in a series of new modes appearing in a comb with intervals Δƒ<sup>(0)</sup> = | ƒ<sub>DAC</sub> − ƒ′|. As the magnetic field <em>H</em> was increased a 1st pre-fractal pattern was observed with frequency interval Δƒ<sup>(1)</sup> = Δƒ<sup>(0)</sup>/2. Finally, the onset of a 2nd pre-fractal was observed with frequency interval Δƒ<sup>(2)</sup> = Δƒ<sup>(1)</sup>/2 = Δƒ<sup>(0)</sup>/4. The magnetic field dependence of the nonlinear signals matched that of the DAC. The spin wave fractal behavior was demonstrated for different values of ƒ′.</p>

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