This is the final version of the article. Available from American Physical Society via the DOI in this record.The response of Y3Fe5O12/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 Y3Fe5O12 (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 1.5 mJ/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.The authors gratefully acknowledge financial support from Engineering and Physical Sciences Research Council Grant No. EP/J018767/1 and an EPSRC CASE award with Dr. D. Williams of Hitachi Cambridge. H.J.M. acknowledges financial support in the form of a scholarship from “The Establishment of Martyrs of Iraq.
