Controlling nanomagnet magnetization dynamics via magnetoelastic coupling

We demonstrate that elastic interactions between nanomagnets in a periodic array can determine the magnetic response according to the nanoscale array geometry. These findings are attributed to magnetoelastic coupling of the spin dynamics with simultaneously excited surface acoustic waves. Specifically, we observe three manifestations of this effect: pinning of the magnetic resonance frequency over an extended range of applied magnetic fields, generation of additional modes whose frequency can differ by more than 100% from the intrinsic element response, and an enhancement of the Fourier amplitude of the magnetic mode at crossovers with mechanical modes. Simulations of the dynamics in the presence of coupling between magnetic and mechanical degrees of freedom are in good agreement with the experiment. This suggests that magnetization dynamics can be controlled by rational structural design on the nanoscale even when the magnetostatic interactions are negligible.

Figure 1

(a) SEM image of nickel nanomagnet arrays indicating array pitch $p$ and orientation of in-plane component of applied magnetic field; (b) schematic side view of nanomagnet array showing substrate structure and two-color pump-probe arrangement with the differently sized pump and probe pulses.

Figure 2

(a)–(c) Background-subtracted TR-MOKE signal measured on (a) a nickel film, (b) an array of aluminum elliptic disks, and (c) an array of nickel elliptic disks for $H_{\mathrm{app}}=2\mathrm{kOe}$. The left and the center columns show the oscillations of the magnetic and nonmagnetic channels, respectively, plotted on the same scale for each sample. The right column shows the Fourier spectra of the magnetic (black) and nonmagnetic (light gray) signals. In (b) and (c), the dark and gray arrows show the predicted RW and SSLW frequencies, respectively. (d) Normalized Fourier spectra measured on the nickel film at different applied fields. The dashed line represents the fit with the Kittel equation.

Figure 3

Fourier spectra for nickel elliptic disks for $p=212\mathrm{nm}$. (a) Measured nonmagnetic signal. (b), (d) Measured magnetic signal. Dashed line is the simulation result for nickel elliptic disks without magnetoelastic contribution. The solid and dashed arrows in (b) indicate the RW and SSLW frequencies. (c), (e) Simulated magnetization dynamics including magnetoelastic coupling. The Fourier amplitudes in (a), (b), and (c) are normalized for better visualization of oscillation modes. The nonnormalized Fourier spectra in (d) and (e) illustrate the enhanced Fourier amplitude at the crossover points at 12.2, 15.8, 17.7, and 22.3 GHz.

Figure 4

Fourier spectra for nickel elliptic disks for $p=282\mathrm{nm}$. (a) Measured nonmagnetic spectra. (b), (d) Measured magnetic spectra. The solid and dashed arrows in (b) indicate the RW and SSLW frequencies. (c), (e) Simulated magnetization dynamics with magnetoelastic coupling. The Fourier amplitudes in (a), (b), and (c) are normalized.