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. 2017 Sep 6;7(1):10600.
doi: 10.1038/s41598-017-11099-y.

Spectral Control of Elastic Dynamics in Metallic Nano-Cavities

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Free PMC article

Spectral Control of Elastic Dynamics in Metallic Nano-Cavities

Henning Ulrichs et al. Sci Rep. .
Free PMC article

Abstract

We show how the elastic response of metallic nano-cavities can be tailored by tuning the interplay with an underlying phononic superlattice. In particular, we exploit ultrafast optical excitation in order to address a resonance mode in a tungsten thin film, grown on top of a periodic MgO/ZrO2 multilayer. Setting up a simple theoretical model, we can explain our findings by the coupling of the resonance in the tungsten to an evanescent surface mode of the superlattice. To demonstrate a second potential benefit of our findings besides characterization of elastic properties of multilayer samples, we show by micromagnetic simulation how a similar structure can be utilized for magneto-elastic excitation of exchange-dominated spin waves.

Conflict of interest statement

The authors declare that they have no competing interests.

Figures

Figure 1
Figure 1
Sample and method. (a) TEM image from SL1, obtained in the center of the sample. (b) XRR spectrum. (c) Sketch of the optical pump-probe experiment. (d) Time-resolved reflectivity data, obtained at the same lateral position as the TEM images.
Figure 2
Figure 2
Elastic dynamics on SLs terminated by tungsten wedges. (a) Time-dependent reflectivity (background subtracted), obtained at different locations on SL1, and thereby at different W thicknesses, and (b) corresponding Fourier power spectra. (c) Power spectra, determined from reflectivity measurement from SL 2. (df) Show further analysis of the dynamics found on SL 1. (d) Dependence of peak power, (e) central peak frequency, and (f) life time on the tungsten layer thickness.
Figure 3
Figure 3
Analytical modelling of elastic dynamics in SL1. (a) Band structure diagram showing londitudinal waves in an idealized infinite SL, calculated from solving Eq. (2), and the dispersion of the surface resonance in a terminated SL (closed circle). (b) Thickness dependence of frequency and imaginary wave number of the surface resonance. (c) Analytically determined stress |σ(z)| profile of the resonance in the tungsten layer and it’s tail in the SL for t W = 15 nm.
Figure 4
Figure 4
Micromagnetic simulation of elastically driven spin-wave resonance in a magneto-elastic capping layer (CoFeB). (a) Thickness dependence of resonance frequencies, calculated by Eqs (6) and (7). Dashed lines indicate the intersection at a thickness of 14.25 nm and a frequency of 184 GHz. (b) Normalized profile of elastic surface wave resonance in the CoFeB layer (red curve), used as input for micromagnetic simulation, and resulting normalized profile of the spin wave resonance (blue curve). (c) Fourier amplitude spectra of the elastically driven spin dynamics in the center of the CoFeB film as a function of the external field. The dashed line indicates the frequency of the driving elastic wave.

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