Effect of annealing on the structure and magnetic properties of Co2FeAl0.5Si0.5 thin films on Ge(111)

We present a magnetic and structural properties study of epitaxially grown B2-ordered full Heusler Co2FeSi0.5Al0.5 single crystal films on Ge(111) substrates, as a function of annealing temperature. Hysteresis loop measurements reveal that the magnetic properties of Co2FeSi0.5Al0.5 are stable up to 450 °C while ferromagnetic resonance linewidth measurements show a reduction of Gilbert damping from 5.6 × 10−3 to 2.9 × 10−3 for as-grown and annealed film, respectively. Above 500 °C, the films have increased coercivity, decreased saturation magnetisation, and show characteristic two-magnon scattering resonance line-shapes. Magnetic inhomogeneities developed within the film when annealed above 500 °C were correlated to significant interdiffusion at the film-substrate interface, as confirmed by scanning transmission electron microscopy and electron energy loss spectroscopy. By performing first-principles calculations based on atomistic models developed from atomically-resolved microscopy images, we show the magnetic moment of the Co2FeSi0.5Al0.5 film reduces upon Co substitution by Ge atoms.