Ferromagnetic resonance of permalloy artificially nanostructured films

The deposition of a ferromagnetic material on top of a patterned template can be used to produce artificially structured magnetic films. Nanochannel alumina wafers with pore sizes of 20 nm, 100 nm and 200 nm have been used to sputter deposit permalloy (Ni₈₁Fe₁₉ ) films in the thickness range 5-100 nm. The films tend to grow on top of the walls separating the nanochannels and mimic the network-like surface topography. Using ferromagnetic resonance techniques we have characterized these films and reference films deposited on flat glass substrates. For the films deposited on 20 nm pore size wafers it was found that the anisotropy easy axis was always parallel to the film plane. The demagnetization factors and the particle aspect ratio were calculated assuming prolate (rod-like) and oblate (disk-like) spheroids. The thinner films behave as a collection of rods with an aspect ratio between 1.2 and 2. Thick films, on the other hand, behave as flat disks with an aspect ratio of ~12. The measured absorption linewidths are consistent with these observations