Thickness-dependent magnetic properties in Pt/Co/Ni _n multilayers with perpendicular magnetic anisotropy

We systematically investigated the Ni and Co thickness-dependent perpendicular magnetic anisotropy (PMA) coefficient, magnetic domain structures, and magnetization dynamics of Pt(5 nm)/Co( t _Co)/Ni( t _Ni) ₅/Pt(1 nm) multilayers by combining the four standard magnetic characterization techniques. The magnetic-related hysteresis loops obtained from the field-dependent magnetization M and anomalous Hall resistivity (AHR) ρ _xy showed that the two serial multilayers with t _Co = 0.2 nm and 0.3 nm have the optimum PMA coefficient K _U as well as the highest coercivity H _C at the Ni thickness t _Ni = 0.6 nm. Additionally, the magnetic domain structures obtained by magneto-optic Kerr effect (MOKE) microscopy also significantly depend on the thickness and K _U of the films. Furthermore, the thickness-dependent linewidth of ferromagnetic resonance is inversely proportional to K _U and H _C, indicating that inhomogeneous magnetic properties dominate the linewidth. However, the intrinsic Gilbert damping constant determined by a linear fitting of the frequency-dependent linewidth does not depend on the Ni thickness and K _U. Our results could help promote the PMA Co/Ni multilayer applications in various spintronic and spin-orbitronic devices.