Thermally induced magnetization dynamics of optically excited YIG / Cu / Ni₈₁Fe₁₉ trilayers

The response of Y₃Fe₃O₁₂ / Cu / Ni₈₁Fe₁₉ trilayer structures to excitation by a femtosecond laser pulse has been studied in optical pump-probe experiments and compared with the response of Y₃Fe₃O₁₂ (YIG) and Ni₈₁Fe₁₉ reference samples. The optical pump induces a partial demagnetization of the Ni₈₁Fe₁₉ , a large thermal gradient within the YIG, and temperature differences across the interfaces within the sample stack. When a moderate magnetic field is applied close to normal to the sample plane, so as to quasialign the YIG magnetization with the field and cant the Ni₈₁Fe₁₉ magnetization from the plane, ultrafast demagnetization initiates precession of the Ni₈₁Fe₁₉ magnetization. The transient temperature profile within the samples has been modeled using a one-dimensional finite-element computational model of heat conduction, while the magnetization dynamics are well described by a macrospin solution of the Landau-Lifshitz-Gilbert equation. The precessional response of the Ni₈₁Fe₁₉ layers within the trilayers and the Ni₈₁Fe₁₉ reference sample are very similar for pump fluences of up to 1.5mJ /cm² , beyond which irreversible changes to the magnetic properties of the films are observed. These results suggest that the spin Seebeck effect is ineffective in modifying the precessional dynamics of the present YIG / Cu / Ni₈₁Fe₁₉ samples when subject to ultrafast optical excitation.