  Time-resolved x-ray diffraction has been used to measure the low-temperature
thermal transport properties of a Pt/Gd3Fe5O12//Gd3Ga5O12 metal/oxide
heterostructure relevant to applications in spin caloritronics. A pulsed
femtosecond optical signal produces a rapid temperature rise in the Pt layer,
followed by heat transport into the Gd3Fe5O12 (GdIG) thin film and the
Gd3Ga5O12 (GGG) substrate. The time dependence of x-ray diffraction from the
GdIG layer was tracked using an accelerator-based femtosecond x-ray source. The
ultrafast diffraction measurements probed the intensity of the GdIG (1 -1 2)
x-ray reflection in a grazing-incidence x-ray diffraction geometry. The
comparison of the variation of the diffracted x-ray intensity with a model
including heat transport and the temperature dependence of the GdIG lattice
parameter allows the thermal conductance of the Pt/GdIG and GdIG//GGG
interfaces to be determined. Complementary synchrotron x-ray diffraction
studies of the low-temperature thermal expansion properties of the GdIG layer
provide a precise calibration of the temperature dependence of the GdIG lattice
parameter. The interfacial thermal conductance of the Pt/GdIG and GdIG//GGG
interfaces determined from the time-resolved diffraction study is of the same
order of magnitude as previous reports for metal/oxide and epitaxial dielectric
interfaces. The thermal parameters of the Pt/GdIG//GGG heterostructure will aid
in the design and implementation of thermal transport devices and
nanostructures.
