Shape effects in the ferromagnetic resonance of nanosize rectangular Permalloy arrays

In-plane and out-of-plane ferromagnetic resonance measurements were performed on arrays of Permalloy rectangles, prepared by interference lithography. In the absence of crystalline anisotropy, the shape anisotropy dominates the angular dependence of the resonance and the linewidth. The 60-70-mT in-plane anisotropy follows the increase of the aspect ratio. The uniaxial out-of-plane anisotropy fields are on the order of 500 mT. The linewidth has a strong angular dependence, both in the in- and out-of-plane rotation, ranging from about 17 to 23 mT along the easy and hard axes and decreasing with increasing shape anisotropy. Two distinct resonance modes observed in the perpendicular orientation are associated with the main volume mode and shape mode of magnetostatic origin.