Effect of surface morphology on magnetization dynamics of cobalt ultrathin films: An in-situ investigation

Growth of Co film on SiO2/Si substrates with surface roughness of 0.5 nm and 1.6 nm have been studied in-situ using magneto-optical Kerr effect (MOKE) and transport measurements. In-situ measurements jointly suggest that the films grow via Volmer-Weber growth process and proceed via a nonmagnetic, superparamagnetic and a ferromagnetic phase formation on both the substrates. Islands are found to coalesce at film thicknesses similar to 0.6 nm and at similar to 1.5 nm with continuous film formation around film thickness similar to 1.5 nm and similar to 3.0 nm for smooth and rough substrates, respectively. Ferromagnetic long-range ordering i.e., appearance of magnetic hysteresis loop in both films is observed just after coalesce stage. Observed azimuthal angular dependence of coercivity confirmed the presence of a weak uniaxial magnetic anisotropy (UMA) in both the films, whereas difference in UMA with substrate roughness is interpreted in terms of combined effect of domain wall pinning and internal stresses in the films. Origin of much higher UMA in case of the Co film deposited on ripple patterned substrate of similar root mean square roughness is attributed to the modified long range dipolar stray fields on the surface.

Automated summary

The growth of Co film on SiO2/Si substrates with different surface roughness was analyzed using MOKE and transport measurements. The films were found to grow via Volmer-Weber process, leading to the formation of continuous ferromagnetic films with thicknesses around 1.5 nm. The presence of weak uniaxial magnetic anisotropy in the films was confirmed, with differences attributed to the effects of domain wall pinning and internal stresses, particularly on ripple patterned substrates.