We report the magnetic dynamics of as-deposited $\mathrm{M}{\mathrm{n}}_2\mathrm{Au}/\mathrm{CoFeB}$ heterostructures via time-resolved magneto-optical Kerr effect spectroscopy. Increasing the pump fluence from 5 to $25\mathrm{mJ}/\mathrm{c}{\mathrm{m}}^2$ results in an effective demagnetization field $4\pi M_{\text{eff}}$ decreasing from 9.178 to 7.483 kOe, accompanied by magnetic damping ${\alpha }_0$ decreasing from 0.0225 to 0.0110. The concomitant modulation of $4\pi M_{\text{eff}}$ and ${\alpha }_0$ is elucidated through the mechanism that the pump excitation with elevated fluence suppresses the antiferromagnetic (AFM) order of $\mathrm{M}{\mathrm{n}}_2\mathrm{Au}$ and antiferromagnetic-ferromagnetic (AFM-FM) exchange coupling by thermal effect, thereby reducing both $4\pi M_{\text{eff}}$ and ${\alpha }_0$. These findings provide critical insights into femtosecond laser-modulated magnetic dynamics of AFM/FM bilayers and pave the way for AFM/FM applications in spintronics.

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• Magnetic coupling
• Magnetic interactions
• Magnetism
• Magneto-optical Kerr effect