A large magnetoresistance is expected when half-metallic ferromagnets are used in magnetic tunneling junctions with polycrystalline AlOx barrier. We demonstrate by in situ tunneling microscopy how the atomically smooth morphology of Co2Cr0.6Fe0.4Al Heusler thin films results in unfavorable wetting properties of the Al layer, which forms the tunneling barrier after oxidation. The insertion of a very thin (2.5 Å) Mg layer at the Co2Cr0.6Fe0.4Al/Al interface changes the growth mode of the Al drastically. As a result the tunneling magnetoresistance (TMR) is clearly enhanced [Co2Cr0.6Fe0.4Al/AlOx/Co70Fe30 junction: TMR(4 K)=101%]. The corresponding Jullière spin polarization amounts to 67%, larger than previously reported values for this compound.
The thermal magnonic spectra of Co2Cr0.6Fe0.4Al (CCFA) and Co2FeAl were investigated using Brillouin light scattering (BLS) spectroscopy. For CCFA, the exchange constant A (exchange stiffness D) is found to be 0.48 ± 0.04 µerg cm−1 (203 ± 16 meV Å2), while for Co2FeAl the corresponding values of 1.55 ± 0.05 µerg cm−1 (370 ± 10 meV Å2) were found. The observed asymmetry in the BLS spectra between the Stokes and anti-Stokes frequencies was assigned to an interplay between the asymmetrical profiles of hybridized Damon–Esbach and perpendicular standing spin-wave modes, combined with the optical sensitivity of the BLS signal to the upper side of the CCFA or Co2FeAl film.
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