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We present measurements of thermal and electrical conductivity of polycrystalline permalloy (Ni-Fe), aluminum, copper, cobalt, and nickel thin films with thickness < 200 nm. A micromachined silicon-nitride membrane thermal isolation platform allows measurements of both transport properties on a single film and an accurate probe of the Wiedemann-Franz (WF) law expected to relate the two. Through careful elimination of possible effects of surface scattering of phonons in the supporting membrane, we find excellent agreement with WF in a thin Ni-Fe film over nearly the entire temperature range from 77 to 325 K. All other materials studied here deviate somewhat from the WF prediction of electronic thermal conductivity with a Lorenz number, L, suppressed from the free-electron value by 10 − 20%. For Al and Cu we compare the results to predictions of the theoretical expression for the Lorenz number as a function of T . This comparison indicates two different types of deviation from expected behavior. In the Cu film, a higher than expected L at lower T indicates an additional thermal conduction mechanism, while at higher T lower than expected values suggests an additional inelastic scattering mechanism for electrons. We suggest the additional low T L indicates a phonon contribution to thermal conductivity, and consider increased electron-phonon scattering at grain boundaries or surfaces to explain the high T reduction in L.

We present measurements of spin pumping detected by the inverse spin Hall effect voltage and ferromagnetic resonance spectroscopy in a series of metallic ferromagnet/normal metal thin film stacks. We compare heterostructures grown in situ to those where either a magnetic or nonmagnetic oxide is introduced between the two metals. The heterostructures, either nickel with a platinum overlayer (Ni/Pt) or the nickel-iron alloy permalloy (Py) with a gold overlayer (Py/Au), were also characterized in detail using grazing-incidence X-ray reflectivity, Auger electron spectroscopy, and both SQUID and alternating-gradient magnetometry. We verify the presence of oxide layers, characterize layer thickness, composition, and roughness, and probe saturation magnetization, coercivity, and anisotropy. The results show that while the presence of a non-magnetic oxide at the interface suppresses spin transport from the ferromagnet to the non-magnetic metal, a thin magnetic oxide (here the native oxide formed on both Py and Ni) somewhat enhances the product of the spin mixing conductance and the spin Hall angle. We also observe clear evidence of an out-of-plane component of magnetic anisotropy in Ni/Pt samples that is enhanced in the presence of the native oxide, resulting in perpendicular exchange bias. Finally, the dc inverse spinHall voltages generated at ferromagnetic resonance in our Py/Au samples are large, and suggest values for the spin Hall angle in gold of 0.04 < α SH < 0.22, in line with the highest values reported for Au. This is interpreted as resulting from Fe impurities. We present indirect evidence that the Au films described here indeed have significant impurity levels.2

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Measurements of thermoelectric effects such as the Seebeck effect, the generation of electric field in response to an applied thermal gradient, are important for a range of thin films and nanostructures used in nanoscale devices subject to heating. In many cases, a clear understanding of the fundamental physics of these devices requires knowledge of the intrinsic thermoelectric properties of the material, rather than the so-called “relative” quantity that comes directly from measurements and always includes contributions from the voltage leads. However, for a thin film or nanostructure, determining the absolute Seebeck coefficient, αabs, is challenging. Here, we first overview the challenges for measuring αabs and then present an approach for determining αabs for thin films from relative measurements made with a micromachined thermal isolation platform at temperatures between 77 and 350K. This relies on a relatively simple theoretical description based on the Mott relation for a thin film sample as a function of thickness. We demonstrate this technique for a range of metal thin films, which show that αabs almost never matches expectations from tabulated bulk values, and that for some metals (most notably gold) even the sign of αabs can be reversed. We also comment on the role of phonon and magnon drag for some metal films.