Structural and nanoacoustic characterization of Co/Pt ferromagnetic superlattices

Superlattices (SLs) with spatially modulated elastic properties-particularly those based on III–V semiconductors-have emerged as key platforms for reaching the ultrahigh-frequency (GHz–THz) regime in nanoacoustic devices. The exploration of alternative materials with multifunctional properties remains a rich and promising area of research. In this work, we investigate the structural, magnetic, and acoustic properties of nanometric Co/Pt SLs. X-ray reflectometry reveals a well-defined periodicity, while scanning transmission electron microscopy combined with local compositional analysis shows that the SLs exhibit a compositional modulation rather than sharp interfaces. The polycrystalline nature of the structures is confirmed by both x-ray diffraction and transmission electron microscopy. Magnetization measurements indicate the presence of perpendicular magnetic anisotropy at higher Co concentrations. Picosecond acoustic experiments demonstrate that the SLs support short-lived acoustic modes up to 900 GHz, along with up to seven acoustic echoes with frequencies ranging from 40 to 250 GHz. These findings open a path toward investigating phonon-driven magnetization dynamics in such structures, establishing a foundational step toward the development of magnetoacoustic devices operating at ultrahigh frequencies.