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

Abstract

We report on the first observation of an exact fractal pattern in the time-domain arising spontaneously from a dynamic artificial crystal (DAC). The all-magnon process occurs in a passive, unlithographed magnetic waveguide. The DAC was created by a standing spin wave of frequency $f_{\mathrm{DAC}}$ in a region of nonlinear waveguide, resulting in a spatio-temporally periodic potential. The interaction of travelling spin waves of frequency $f^{\prime }$ with the DAC resulted in a series of new modes appearing in a comb with intervals $\Delta f^{(0)}=\mid f_{\mathrm{DAC}}-f^{\prime }\mid$. As $H$ was increased a 1st pre-fractal pattern was observed with frequency interval $\Delta f^{(1)}=\Delta f^{(0)}/2$. Finally, the onset of a 2nd pre-fractal was observed with frequency interval $\Delta f^{(2)}=\Delta f^{(1)}/2=\Delta f^{(0)}/4$. The magnetic field dependence of the nonlinear signals effect matched that of the DAC. The fractal-like behavior was demonstrated for different values of $f^{\prime }$.

7 pages, 10 figures