Structural and magnetic properties of thin cobalt films with mixed hcp and fcc phases

Cobalt is a magnetic material that finds extensive use in various applications, ranging from
magnetic storage to ultrafast spintronics. Usually, it exists in two phases with different crystal lattices, namely in
hexagonal close-packed (hcp) or face-centered cubic (fcc) structure. The crystal structure of Co films
significantly influences their magnetic and spintronic properties. We report on the thickness dependence of the
structural and magnetic properties of sputter-deposited Co on a Pt seed layer. It grows in an hcp lattice at low
thicknesses, while for thicker films, it becomes a mixed hcp-fcc phase due to a stacking fault progression along
the growth direction. The X-ray based reciprocal space map technique has been employed to distinguish and
confirm the presence of both phases. Moreover, the precise determination of Landé’s g-factor by ferromagnetic
resonance provides valuable insights into the structural properties. In our detailed experiments, we observe
that a structural variation results in a nonmonotonic variation of the magnetic anisotropy along the thickness.
The work offers information of great significance and insight for both fundamental physics and potential
applications of thin films with perpendicular magnetic anisotropy.