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

[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 Fe
₃
O
₄
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 Fe
₃
O
₄
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 Fe
₃
O
₄
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 Fe
₃
O
₄
nanoparticles significantly modifies the magnetization dynamics of Co/Ni multilayer.