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中国物理学会期刊

基于磁性薄膜的磁声耦合频率梳

CSTR: 32037.14.aps.75.20260087

Magnetic frequency comb excited by magnetoacoustic coupling in ferromagnetic films

CSTR: 32037.14.aps.75.20260087
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  • 磁频梳作为一种重要的非线性动力学现象, 在精密频率计量、信号处理及片上磁电子器件中具有重要应用前景, 但传统磁频梳通常依赖强微波驱动和体块磁性材料, 存在功耗高、尺寸大及集成度受限等问题. 本文基于微磁学仿真, 研究了磁性薄膜体系中由表面声波激发的磁声耦合频率梳机制. 通过在具有较大磁弹耦合系数的磁性薄膜上引入驻波声场, 磁振子模式与声子模式发生非线性相互作用, 在无强微波激励条件下形成稳定的磁频梳结构. 系统分析了声波振幅、声波频率、传播方向与磁各向异性轴夹角以及各向异性强度对频率梳特性的影响. 结果表明: 声波频率决定频率梳的齿间距, 声波振幅存在产生频率梳的阈值; 当声波传播方向与磁化稳定方向满足特定角度关系时, 磁弹耦合显著增强, 频率梳强度达到最大; 适中的磁各向异性有利于获得梳齿数量多、频率覆盖范围宽且强度分布均匀的频率梳. 上述研究为实现可调谐、低功耗和高集成度的片上磁频梳器件提供了新的思路.

     

    Magnetic frequency combs (MFCs), which consist of equally spaced spectral lines generated by nonlinear magnetization dynamics, are promising for precision frequency control, broadband signal processing, and on-chip magnonic devices. However, conventional MFCs generally require strong microwave pumping and bulky magnetic resonators, resulting in high power consumption, thermal perturbations, and limited integrability. Here, we propose a low-power route to MFC generation through nonlinear magnetoelastic coupling between a standing surface acoustic wave (SAW) and magnons in a ferromagnetic thin film. Micromagnetic simulations are performed for a 1000 nm × 1000 nm × 5 nm CoFeB film with absorbing boundary regions. The intrinsic response contains a single ferromagnetic-resonance peak near 8 GHz, consistent with the Kittel estimate of 7.86 GHz. When a longitudinal Rayleigh-type standing strain field is applied, the periodically modulated magnetoelastic effective field produces cascaded sidebands. Setting the magnetoelastic coefficients to zero eliminates the comb, confirming that magnetoelastic coupling is the essential generation mechanism.
    The dependences of the comb on SAW strain amplitude, frequency, propagation direction, and magnetic anisotropy are systematically quantified. At a SAW frequency of 2 GHz and a strain amplitude of 2‰, a stable comb with a 2 GHz line spacing is obtained, demonstrating that the repetition frequency is directly set by the acoustic frequency. A clearly resolvable multi-line comb appears at a strain amplitude of approximately 0.1‰; below this observational threshold, only the fundamental acoustic mode and weak low-order mixing components remain. Sweeping the SAW frequency from 0.2 to 2 GHz continuously tunes the line spacing: a 0.2 GHz SAW produces a dense comb spanning about 3 GHz, intermediate frequencies of 0.8–1 GHz yield comparatively uniform line intensities, and a 2 GHz SAW extends the bandwidth beyond 30 GHz, although the high-order lines decay more rapidly. The comb intensity is strongly anisotropic because the magnetoelastic torque depends on the relative orientation of the equilibrium magnetization and SAW propagation direction. In addition, an intermediate uniaxial anisotropy constant of about 2.4 × 104 J/m3 provides the best balance between coherent magnetic alignment and dynamic response; weaker anisotropy (≤2×104 J/m3) leads to nonuniform magnetization, whereas strong anisotropy (>5×104 J/m3) suppresses the precession and reduces the number of comb lines. These findings identify SAW-driven periodic magnetoelastic modulation and nonlinear sideband cascading as the core physics of the MFC and establish an acoustically programmable, low-power, thin-film platform for tunable and highly integrated magnetoacoustic frequency-comb devices.

     

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