Structural, vibrational, and magnetic properties of self-assembled CoPt nanoalloys embedded in SrTiO3

Pulsed laser deposition was used to synthesize vertically aligned nanocomposites (VAN), consisting of ultrathin CoPt nanocolumns embedded in a single crystal SrTiO3 thin film. Combining highresolution transmission electron microscopy (HRTEM), x-ray diffraction (XRD), x-ray absorption spectroscopy (XAS) and molecular dynamics (MD) simulations, we provide an in-depth analysis of the structural and vibrational properties of the CoPt phase over a wide range of concentrations. Despite growing the samples at high temperatures (> 600 • C), we find that the CoPt nanoalloys are characterized by a high degree of structural disorder and complete absence of chemical ordering, even after additional sample annealing. Unexpectedly, for a Co concentration exceeding c(Co) 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. These findings, further confirmed by magnetometry measurements, illustrate the profound impact of vertical epitaxy on the structural and thermodynamic properties of bimetallic CoPt alloys.