We demonstrate the tunability of the ultrafast energy flow in magnetic/nonmagnetic bilayer structures by changing the wavelength of the optical excitation. This is achieved by an advanced description of the temperature-based $\mu T$ model that explicitly considers the wavelength- and layer-dependent absorption profile within multilayer structures. For the exemplary case of a Ni/Au bilayer, our simulations predict that the energy flow from Ni to Au is reversed when changing the wavelength of the excitation from the infrared to the ultraviolet spectral range. These predictions are fully supported by characteristic signatures in the time-dependent magneto-optical Kerr traces of the Ni/Au model system. Our results will open up avenues to steer and control the energy transport in designed magnetic multilayers for ultrafast spintronic applications.

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• Heat transfer
• Magneto-optical Kerr effect
• Spintronics
• Transport phenomena
• Ultrafast magnetization dynamics
• Bilayer films
• Interfaces