Variation of Magnetization Dynamics of Co/Ni Multilayer by Capturing Magnetic Nanoparticles

Abstract

[Co (0.29 nm)/Ni (0.71 nm)]10 multilayers were deposited on Ta (30 nm) and Pt (30 nm) buffer layers, and the variation of the magnetization dynamics by the adsorption of Fe3O4 nanoparticles was studied by vector network analyzer—ferromagnetic resonance method. The surface roughness of the Co/Ni multilayer was 0.52 nm, and significantly increased after the adsorption of the Fe3O4 nanoparticles which was captured by large field gradient on the demagnetized Co/Ni multilayer. The anisotropy field $H_{k}$ , damping constant $\alpha $ , and anisotropy distribution $\Delta H_{k}$ of the Co/Ni on Ta buffer layer were 2.6 kOe, 0.012, and 0.32 kOe, respectively. By adsorbing of the Fe3O4 nanoparticles, the stray field from the nanoparticles $H_{{\text {np}}}$ was applied to the Co/Ni, and $H_{k} + {H}_{{\text {np}}}$ was estimated to increase to 3.7 kOe. Moreover, $\alpha $ and $\Delta H_{k}$ also increased to 0.020 and 0.42 kOe by the adsorption, respectively. Similarly, $H_{k} + H_{\mathrm{np}}$ , $\alpha $ , $\Delta H_{k}$ of Pt buffered Co/Ni also increased from 2.4 kOe, 0.033, 0.43 kOe to 4.2 kOe, 0.055, 0.53 kOe, respectively. These results suggest that the adsorption of Fe3O4 nanoparticles significantly modifies the magnetization dynamics of Co/Ni multilayer.