Professor John Gregg

Abstract:

<jats:p>We study surface acoustic waves (SAWs) in yttrium iron garnet (YIG)/zinc oxide (ZnO) heterostructures, comparing the results of a computationally lightweight analytical model with time-resolved microfocused Brillouin light scattering (<a:math xmlns:a="http://www.w3.org/1998/Math/MathML" display="inline" overflow="scroll"><a:mtext fontfamily="times">μ</a:mtext></a:math>-BLS) data. Interdigital transducers (IDTs), with operational frequencies in the gigahertz regime, were fabricated on 50-nm and 100-nm thin films of YIG prior to sputter deposition of 830-nm and 890-nm films of piezoelectric ZnO. We find good agreement between our analytical model and <e:math xmlns:e="http://www.w3.org/1998/Math/MathML" display="inline" overflow="scroll"><e:mtext fontfamily="times">μ</e:mtext></e:math>-BLS data of the IDT frequency response and SAW group velocity, with clear differentiation between the Rayleigh-like and Sezawa-like modes. Finally, nonreciprocal coupling between SAWs and spin waves (SWs) is shown. This work paves the way for a detailed study of the interaction between SAWs and SWs in low SW damping YIG, with the possibility of a method for future energy-efficient SW excitation.</jats:p> <jats:sec> <jats:title/> <jats:supplementary-material> <jats:permissions> <jats:copyright-statement>Published by the American Physical Society</jats:copyright-statement> <jats:copyright-year>2025</jats:copyright-year> </jats:permissions> </jats:supplementary-material> </jats:sec>

Abstract:

We propose and experimentally demonstrate a means of broadband phonon-magnon interconversion that relies on combining magnetoelastic coupling with translational symmetry breaking in the important experimental material yttrium iron garnet (YIG). As well as being of interest for its basic physics, this quasiparticle coupling mechanism adds to the range of effects that potentially find useful application in hybrid solid-state quantum computing devices as well as low-power wave-based classical computing architectures.

Abstract:

Apparatus for generating spin waves comprising a body (102) of magnetic material and an elastic wave generator (120), wherein the body (102) has a surface (108) and the elastic wave generator (120) is arranged to transmit elastic waves so that they propagate through the body (102) towards the …

Abstract:

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_DAC 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⁽⁰⁾ = | ƒ_DAC − ƒ′|. As the magnetic field H was increased a 1st pre-fractal pattern was observed with frequency interval Δƒ⁽¹⁾ = Δƒ⁽⁰⁾/2. Finally, the onset of a 2nd pre-fractal was observed with frequency interval Δƒ⁽²⁾ = Δƒ⁽¹⁾/2 = Δƒ⁽⁰⁾/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′.