Electron scattering at interfaces in Ru(0001)/Co(0001) multilayers

Electron transport measurements on 60-nm-thick multilayers containing N = 2-58 individual Ru and Co layers are employed to quantify the specific resistance of Ru/Co interfaces. Sputter deposition on AlO(0001) at T = 400 °C leads to a 0001 preferred orientation with x-ray diffraction (XRD) Ru and Co 0002 peaks that shift closer to each other with increasing N, suggesting interfacial intermixing. The intermixing is quantified by x-ray reflectivity (XRR) and confirmed by an XRD Ru/Co alloy peak that develops during in situ synchrotron annealing as well as for deposition at a higher T = 600 °C. The room-temperature resistivity increases from 15.0 to 47.5 μΩ cm with decreasing superlattice period Λ = 60-2 nm. This is attributed to increasing electron scattering at the intermixed metal interfaces. The transport data are well described by a parallel conductor model that treats metal layers and the intermixed alloy as parallel resistors, where the resistivity of the intermixed alloy of 60.4 μΩ cm is determined from a co-deposited Ru/Co sample. Data fitting provides values for the effective thickness of the intermixed interface of 16.8 nm, in good agreement with the XRR value, yielding a Ru/Co contact resistance of 8.5 × 10⁻¹⁵ Ω m² for interfaces deposited at 400 °C. The overall results show that the Ru/Co contact resistance is dominated by a high-resistivity interfacial alloy and, therefore, is a strong function of the deposition process, particularly the processing temperature.