Annealing Temperature and Thickness Dependencies of Perpendicular Magnetic Anisotropy and Dzyaloshinskii-Moriya Interaction of Pt/Co/MgO thin films

Effects of the ferromagnetic layer thickness and annealing temperature were studied in Pt/Co/MgO-based systems grown on thermally oxidized Si substrates using magnetron sputtering system. The Co thicknesses were varied in the range 1-6 nm and the samples were annealed ex situ at 200, 300 and 400°C. Vibrating sample magnetometer was used to determine the magnetization at saturation and the magnetic dead layer thickness that were found to be insignificantly affected by the annealing. Brillouin light scattering, in Damon-Eshbach configuration, was used to measure the thermally excited spin wave frequencies versus the in-plane applied magnetic field and the spin wave vector which were used to investigate the perpendicular magnetic anisotropy (PMA) and interfacial Dzyaloshinskii-Moriya interaction (iDMI), respectively. The Co effective thickness dependence of the effective magnetization (Meff), which provides information on the PMA constants, shows the existence of two linear regimes with different slopes due to misfit strain induced magnetoelastic anisotropy contributions to volume and surface terms. The volume magnetocrystalline anisotropy constant increases monotonously with annealing temperature whereas the pure surface (Neel type) constant increases with annealing up to 300°C and degrades at 400°C. The surface iDMI constant decreases with increasing annealing temperature and no obvious correlation with interface PMA constant has been found, suggesting different interfaces contribution to PMA and iDMI.