Relation Between Static and Dynamic Magnetization Effects and Resonance Behavior in Ni Nanowire Arrays

The dynamic properties of arrays of 1-D nickel nanowires (NWs) with high aspect ratio have been studied by ferromagnetic resonance technique using a flip-chip method in the frequency domain. The fundamental magnetic parameters such as spontaneous magnetization, gyromagnetic ratio (y), Gilbert damping (α), and magnetic anisotropies of the NWs of various lengths were determined from resonance frequency - field [ f_res(H₀)] and frequency linewidth - field [Δf_res(H₀)] data. The effective fields of the NW system were observed to decrease slightly with the increasing length of NWs. The value of gyromagnetic ratio (y) increases from shorter length NWs and then saturates above 16 μm length NWs. From the Δf_res(H₀) data, we quantitatively determined Gilbert damping (α). The value of α first increases for smaller lengths and then saturates for higher lengths >30 μm, which may be attributed to intrinsic and extrinsic relaxation contributions to linewidth. We observed the dc current (I_DC) effects on RF properties [ f_res(I_DC) and Δf_res (I_DC) data] of coplanar waveguide (CPW)-based NW structures. Resonance frequency as well as frequency linewidth decreased with increase in I_DC. We conclude that the Joule heating effect causes increase in temperature, which decreases saturation magnetization and anisotropy field (H_ani), and hence there is a decrease of f_res and Δf_res with the increase of I_DC.