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[论文解读] Optical probing of magnons and phonons in Ni80Fe20 nanodot arrays

A. M. H. G. Adhikari, P. Graczyk|arXiv (Cornell University)|Jan 15, 2026
Magnetic properties of thin films被引用 0
一句话总结

该论文演示了 Ni80Fe20 纳米点阵列中偶极自旋（自旋子）与弹性（声子）模态的全光激发与探测，揭示了取决于晶格几何的磁弹耦合，并显示由于布里渊区折叠在 k=0 处的驻留表面声波（SAW）。

ABSTRACT

Control of collective spin excitations by static or dynamic strain is an emerging phenomenon that requires in-depth understanding for design of future spin-wave-regulated devices. Here, we explore mutually interacting spin waves and acoustic wave modes in addition to few non-interactive modes through all optical excitation in ordered arrays of Ni80Fe20 nanomagnets. The acoustic wave originated from elastic deformation resonantly couple to the spin wave via magnetoelastic effect at their overlapping frequency. We demonstrate that the choice of the lattice type in which the magnetic nanodots are arranged is crucial for the observation of the magnetoelastic interaction. Therefore, the study shows that the simultaneous existence of elastic wave and spin wave offer ingeneously advantageous features to pave the way of energy-efficient magnetoacoustic devices.

研究动机与目标

  • Understand how static and dynamic strain mediates magnetoelastic coupling between spin waves and acoustic waves in Ni80Fe20 nanodot arrays.
  • Identify how lattice geometry (square vs hexagonal) influences magnon-phonon interactions.
  • Characterize SAW and SW modes experimentally and corroborate with numerical simulations.
  • Determine which modes couple and under what conditions, to inform magnetoacoustic device design.

提出的方法

  • Fabricate 200 nm Ni80Fe20 (Permalloy) nanodot arrays arranged in hexagonal or square lattices with 350 nm lattice constant on Si/SiO2 substrates.
  • Excite and detect elastic and magnetic vibrations with a two-color femtosecond pump-probe TR-MOKE setup; pump at 400 nm, probe at 800 nm, at a 1 kHz chopped pump modulation.
  • Model ME dynamics by coupling elastodynamic and Landau-Lifshitz equations; implement in COMSOL FEM with Bloch boundary conditions and a Love/ Rayleigh/ Sezawa SAW analysis.
  • Use perturbative field and external pressure stimuli to compute magnon and phonon responses and compare calculated mode intensities I_p and I_m to experiment.
Figure 1: Scanning electron micrographs of Py nanodots forming (a) hexagonal and (b) square lattice. For both samples, the size of the nanodots $d=200$ nm, is fixed, and the spacing between them $s$ is selected to set the lattice constant, $a=$ 350 nm. (c) Schematic illustration of measurement geome
Figure 1: Scanning electron micrographs of Py nanodots forming (a) hexagonal and (b) square lattice. For both samples, the size of the nanodots $d=200$ nm, is fixed, and the spacing between them $s$ is selected to set the lattice constant, $a=$ 350 nm. (c) Schematic illustration of measurement geome

实验结果

研究问题

  • RQ1Can magnetoelastic coupling occur between standing SAWs and SWs in patterned Py nanodot arrays, and how does lattice geometry affect it?
  • RQ2How do SAW and SW mode spectra depend on lattice type (square vs hexagonal) and interdot spacing?
  • RQ3What are the spatial profiles and polarization characteristics of identified SAW and SW modes?
  • RQ4Under what conditions do SAW and SW modes exhibit frequency overlap or avoided crossings, indicating ME coupling?

主要发现

  • Four distinct SAW modes (E1–E4) appear in 5–20 GHz range, with E2 strongest and E1/E2 well separated from E3/E4.
  • SW spectra show field-dependent and field-independent modes; an overlap between M2 (SW) and E2 (SAW) at certain fields suggests potential ME coupling.
  • Lattice geometry strongly influences ME interaction; square lattices show reduced E3/E4SAW frequencies and enable stronger SEZAWA/Rayleigh-type interactions compared to hexagonal lattices.
  • Numerical FEM simulations identify SAW modes as Rayleigh and Sezawa types and SW modes as edge (Me) and fundamental (Mf) modes, with ME field profiles revealing coupling mechanisms.
  • In square lattices, Sezawa and Rayleigh components contribute to enhanced magnetization dynamics near crossings with Mf, mediated by intermediate modes such as Rxy.
  • The ME interaction is sensitive to lattice symmetry and dispersion folding into the first Brillouin zone, enabling ME coupling for standing waves at k=0 in the patterned structure.
Figure 2: Background subtracted time-resolved (a) reflectivity and (c) Kerr rotation trace indicating acoustic (SAW) and magnetization (SW) dynamics, respectively, detected for hexagonal lattice of square Py dots on SiO 2 substrate (see Fig. 1 (a)) at magnetic field of $\mu_{0}H_{\rm ext}$ = 185 mT.
Figure 2: Background subtracted time-resolved (a) reflectivity and (c) Kerr rotation trace indicating acoustic (SAW) and magnetization (SW) dynamics, respectively, detected for hexagonal lattice of square Py dots on SiO 2 substrate (see Fig. 1 (a)) at magnetic field of $\mu_{0}H_{\rm ext}$ = 185 mT.

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