Enhanced coercivity of HCP Co–Pt alloy thin films on a glass substrate at room temperature for patterned media

• Deposited Co–Pt alloy thin films on glass substrate at room temperature.
• High out-of-plane coercivity of Co-rich type Co–Pt thin film at thinner thickness.
• Columnar structure contributed out-of-plane coercivity.

High coercivity (Hc) Co-rich type Co–Pt alloy thin films with a columnar grain structure were deposited at room temperature (RT) by magnetron sputtering. Films with a thickness (t) of up to 10 nm had a FCC structure and exhibited soft magnetic properties. When t>25 nm, the magnetic anisotropy changed from in-plane to isotropic. Hc was also enhanced with increasing t and found to be maximum at t=50 nm. The in-plane and out-of-plane Hc of the film was 2.2 and 2.7 kOe, respectively. Further increasing t led to a slight decrease in Hc. Microstructure and phase structure studies revealed columnar Co–Pt grains with a uniform lateral size grown on a 7 nm initial layer. Films with t>25 nm showed a HCP phase, due to the internal stress and volume effect. The microstructural details responsible for the enhanced RT magnetic properties of the HCP Co–Pt alloy thin films were investigated by TEM.