We demonstrate the pumping of phonons by ferromagnetic resonance in a series of ${[\mathrm{Co}\left(0.8\mathrm{nm}\right)/\mathrm{Pd}\left(1.5\mathrm{nm}\right)]}_{\mathrm{n}}$ multilayers ($n=6$, 11, 15, and 20) with strong magnon-phonon coupling and perpendicular magnetic anisotropy. The effect is shown using broadband ferromagnetic resonance over a range of temperatures (10–300 K), where a resonant damping enhancement is observed at frequencies where the phonons can form standing waves across the multilayer. The strength of this effect is enhanced by approximately a factor of 4 at 10 K compared to room temperature, which is anomalous in the sense that the temperature dependence of the magnon-phonon coupling predicts an enhancement that is less than a factor of 2. We conclude by explaining how the stronger-than-expected temperature dependence highlights the essential role of dynamic magnetization pinning in driving the phonons.

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• Magnetization dynamics
• Magnetoelastic effect
• Spin waves
• Magnetic multilayers
• Ferromagnetic resonance