Thermal and electrical characterization of Cu/CoFe superlattices

Abstract

The present work is directed at thermal and electrical characterization of the Cu/CoFe multilayer, which is made of extremely thin periodic layers, using steady-state Joule heating and thermometry in suspended bridges in the temperature range of 50–300 K. The total thickness of the layer is ds=144 nm, while the thickness of individual repeats are 12 and 21 Å for CoFe and Cu layers, respectively. The experimental data for thermal conductivity of a 144-nm-thick single Cu layer is also presented for comparison. The experimental data indicates that the spin-dependent electron scattering at the Cu/CoFe interface contributes to a strong reduction in thermal conductivity of these layers compared to the bulk values. The calculated Lorenz numbers (from the thermal and electrical conductivity data) varies by nearly a factor 2 from 4×10−8 W Ω K−2 at 50 K to 1.8×10−8 W Ω K−2 at 300 K and is different from the free electron value of L0=2.45×10−8 W Ω K−2. This implies that the Wiedemann-Franz law does not hold for Cu/CoFe thin films.