Interfacial thermal transport in spin caloritronic material systems

Abstract

Interfaces often govern the thermal performance of nanoscale devices and nanostructured materials. As a result, accurate knowledge of thermal interface conductance is necessary to model the temperature response of nanoscale devices or nanostructured materials to heating. Here, we report the thermal boundary conductance between metals and insulators that are commonly used in spin-caloritronic experiments. We use time-domain thermoreflectance to measure the interface conductance between metals such as Au, Pt, Ta, Cu, and Al with garnet and oxide substrates, e.g., NiO, yttrium iron garnet (YIG), thulium iron garnet (TmIG), ${\mathrm{Cr}}_{2}{\mathrm{O}}_{3}$, and sapphire. We find that, at room temperature, the interface conductance in these types of material systems range from 50 to $300\phantom{\rule{0.16em}{0ex}}\mathrm{MW}\phantom{\rule{0.16em}{0ex}}{\mathrm{m}}^{\ensuremath{-}2}\phantom{\rule{0.16em}{0ex}}{\mathrm{K}}^{\ensuremath{-}1}$. We also measure the interface conductance between Pt and YIG at temperatures between 80 and 350 K. At room temperature, the interface conductance of Pt/YIG is $170\phantom{\rule{0.16em}{0ex}}\mathrm{MW}\phantom{\rule{0.16em}{0ex}}{\mathrm{m}}^{\ensuremath{-}2}\phantom{\rule{0.16em}{0ex}}{\mathrm{K}}^{\ensuremath{-}1}$ and the Kapitza length is \ensuremath{\sim}40 nm. A Kapitza length of 40 nm means that, in the presence of a steady-state heat current, the temperature drop at the Pt/YIG interface is equal to the temperature drop across a 40-nm-thick layer of YIG. At 80 K, the interface conductance of Pt/YIG is $60\phantom{\rule{0.16em}{0ex}}\mathrm{MW}\phantom{\rule{0.16em}{0ex}}{\mathrm{m}}^{\ensuremath{-}2}\phantom{\rule{0.16em}{0ex}}{\mathrm{K}}^{\ensuremath{-}1}$, corresponding to a Kapitza length of \ensuremath{\sim}300 nm.