Magnetization Dynamics and Reversal Mechanisms in Ni Nanowire and Nanotube Arrays

Highly ordered arrays of Ni nanowires (NWs) and nanotubes (NTs) were electrodeposited into porous anodic alumina templates with 200 nm pore diameter. The geometrical parameters of the NW/NT arrays were tuned by the deposition conditions. The fabricated NWs and NTs had various lengths depending upon deposition time and NTs had a wall thickness of ~40 nm. Morphological characterizations were performed using a scanning electron microscope and transmission electron microscope yields the topology of NWs and NTs, structural properties were determined using X-ray diffraction, and magnetic characterization was done using SQUID. Dynamic properties have been studied by ferromagnetic resonance technique in frequency sweep mode. A comparative study of the magnetization reversal processes was also performed by analyzing the angular variation of resonance frequency of NWs/NTs. The resonance frequency increases linearly with magnetic field for studied arrays. In NWs the magnetization reversal mode is curling mode, whereas for NTs it is coherent rotation mode.