Structural, vibrational, and magnetic properties of self-assembled CoPt nanoalloys embedded in SrTiO3
M Hennes and E Fonda and N Casaretto and J Buchwald and X Weng and G Patriarche and D Demaille and Y Zheng and F Vidal, PHYSICAL REVIEW MATERIALS, 4, 126001 (2020).
Pulsed laser deposition was used to synthesize vertically aligned nanocomposites, consisting of ultrathin CoPt nanocolumns embedded in a single crystal SrTiO3 thin film. Combining high-resolution transmission electron microscopy, x-ray diffraction, x-ray absorption spectroscopy, and molecular dynamics simulations, we provide an in-depth analysis of the structural and vibrational properties of the CoPt phase over a wide range of concentrations. Our findings show that the CoPt nanoalloys are characterized by a high degree of structural disorder and complete absence of chemical ordering, even after additional sample annealing (T similar or equal to 670 degrees C). For a Co concentration exceeding c(Co) similar or equal to 0.55, pole figure measurements unravel a transition from a highly textured short-range disordered fcc phase to a disordered hcp phase with c-axis oriented out of plane, which is at odds with bulk predictions. These findings, further confirmed by magnetometry measurements, illustrate the profound impact of vertical epitaxy on the structural properties of bimetallic CoPt alloys.
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