Ultrafast Measurements of the Interfacial Spin Seebeck Effect in Au and Rare-Earth Iron Garnet Bilayers

TL;DR

This study measures ultrafast interfacial spin currents in Au and rare-earth iron-garnet bilayers using time-resolved optical techniques, revealing a significantly larger spin Seebeck effect in TmIG compared to YIG.

Contribution

It provides the first ultrafast measurements of the interfacial spin Seebeck effect in Au/rare-earth iron-garnet bilayers, highlighting material-dependent differences.

Findings

Spin Seebeck effect is three times larger in Au/TmIG than in Au/YIG.

Interfacial thermal conductance is approximately 3 MW/m^2K.

Ultrafast optical techniques can resolve picosecond spin-current dynamics.

Abstract

We investigate picosecond spin-currents across Au/iron-garnet interfaces in response to ultrafast laser heating of the electrons in the Au film. In the picoseconds after optical heating, interfacial spin currents occur due to an interfacial temperature difference between electrons in the metal and magnons in the insulator. We report measurements of this interfacial longitudinal spin Seebeck effect between Au and rare-earth iron-garnet insulators, i.e. RE$_3$ Fe$_5$O$_{12}$, where RE is Y, Eu, Tb, Tm. We use time domain thermoreflectance (TDTR) measurements to characterize the thermal response of the bilayer to ultrafast optical heating. We use time-resolved magneto-optic Kerr effect (TR-MOKE) measurements of the Au layer to measure the time-evolution of spin accumulation in the Au film. We observe a spin Seebeck effect between Au/TmIG that is three times larger than for an Au/YIG bilayer. The interfacial thermal conductance between electrons in the Au and magnons in the TmIG layer is ~ 3 $\frac{MW}{m^2 K}$.