Pulsed laser deposition was used to synthesize vertically aligned nanocomposites, consisting of ultrathin CoPt nanocolumns embedded in a single crystal ${\mathrm{SrTiO}}_3$ 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 $(T\simeq 670{}^{\circ }\mathrm{C})$. For a Co concentration exceeding $c\left(\mathrm{Co}\right)\simeq 0.55$, 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.

• Received 4 May 2020
• Accepted 30 October 2020

DOI:https://doi.org/10.1103/PhysRevMaterials.4.126001