Correlations between structural, electronic transport, and magnetic properties ofCo2FeAl0.5Si0.5Heusler alloy epitaxial thin films

Abstract

The structural and chemical order are the most important parameters governing the physical properties of the Heusler compounds. Here, we give a comprehensive overview of the correlations between structural and chemical order, electronic transport (longitudinal and transverse) and magnetic (static and dynamic) properties of ${\mathrm{Co}}_{2}{\mathrm{FeAl}}_{0.5}{\mathrm{Si}}_{0.5}$ Heusler alloy epitaxial thin films grown on MgO(001) single-crystal substrates. X-ray diffraction measurements indicated that depending on the annealing temperature the films show $B2$ or $L{2}_{1}$ chemical ordering. Longitudinal magnetoresistivity experiments revealed that for the best $L{2}_{1}$ ordered film, at temperatures bellow $125\phantom{\rule{4pt}{0ex}}\text{K}$, the magnon assisted electronic scattering is quenched indicating the appearance of half-metallicity. The presence of quantum correction in resistivity, whose strength is dependent on the structural ordering, was evidenced at low temperatures. Anomalous Hall experiments indicated that the intrinsic band structure contribution has an opposite sign and that is dominant over the extrinsic skew scattering mechanism. The presence of a small uniaxial magnetic anisotropy contribution superimposed on a larger biaxial one was evidenced via ferromagnetic resonance microstrip line measurements. The biaxial term is well correlated with chemical ordering, having a minimum value for the optimum $L{2}_{1}$ ordered film. The damping parameter was evaluated from ferromagnetic resonance linewidth measurements, and a coefficient as low as $1.9\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}3}$ was found for the $L{2}_{1}$ phase.