Large anomalous Nernst conductivity of L1₀-ordered CoPt in CoPt composition-spread thin films

Abstract

We demonstrate a high-throughput experimental characterization of anomalous Nernst conductivity (αxy A ) of L10-ordered CoPt using Co1–x Pt x composition-spread thin films on MgO(100) substrates. The compositional dependence of the anomalous Nernst effect (ANE), anomalous Hall effect (AHE) and Seebeck effect is systematically measured. As increasing the Pt concentration, the crystal structure in the composition-spread film grown at 500 °C changes from fcc Co, A1-disordered CoPt, L10-ordered CoPt, A1-CoPt to fcc Pt. The largest αxy A of 2.52 A m–1 K–1 is obtained in L10-CoPt for Pt-rich composition of x = 70%, which is larger than that for an additionally fabricated nearly stoichiometric L10-Co48Pt52 reference uniform film. The contribution from direct conversion of a temperature gradient to a transverse charge current through αxy A is dominant to the total anomalous Nernst coefficient compared to the AHE-related contribution. From a scaling analysis of the AHE, the intrinsic contribution is found to be dominant for x = 70%. A theoretical calculation for αxy A of L10-Co50Pt50 agrees with the experimental αxy A value for the nearly stoichiometric reference film by considering on-site Coulomb interaction for Co atoms. We also point out the possible electron doping effect by the addition of Pt in L10-CoPt, which could explain the larger αxy A for the off-stoichiometric Pt-rich composition than that for the nearly stoichiometric one. Our experimental and theoretical results suggest the potential of L10-CoPt with a large αxy A originating from the intrinsic mechanism for future thermoelectric applications.