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
(H
₀
)] and frequency linewidth - field [Δf
_res
(H
₀
)] 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
(H
₀
) 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
.