Ferromagnetic resonance studies of Ni nanowire arrays

Abstract

Using ferromagnetic resonance, the angular dependence of the uniform precession mode of infinite cylinders is investigated at room temperature for low density Ni nanowire arrays, embedded in a polycarbonate membrane, with wire diameters ranging from 35 nm to 500 nm. All wires reveal a very similar behavior of the resonance field vs angle, independent of the wire diameter and wire density, corresponding to the uniform precession mode of an infinite cylinder including the shape demagnetization anisotropy and a small uniaxial anisotropy contribution. From the analysis of the angular dependence of the linewidth, the distribution of the wire orientation and the effective anisotropy field can be estimated. The latter is broadened due to the presence of a sub-structure in the absorption spectra.

Theory of Spin Excitations and the Microwave Response of Cylindrical Ferromagnetic Nanowires

“…We also have presented studies of both the excitations in and the microwave response of samples quite similar to those explored in Ref. 1, and compared the differences between the wire and the well know case of the thin film. We conclude with some additional remarks.…”

“…This is illustrated in spectra taken by Ebels and Wigen. 1 These authors explore the FMR spectra of Ni nanowires with radius 350, 800, 2700, and 5000 Å. With the exception of the 800 Å sample, a single absorption line is observed.…”

“…We have assumed the frequency is 34.4 GHz, as utilized in Ref. 1. Thus, the resonance field is a bit above 8 kG, for our parameters.…”

“…There should then be strong interactions between nanowires, in dense arrays such as those explored by Ebels and Wigen. 1 The consequence of these interactions is not explored here, though our formal structure can be used for this purpose.…”

“…1 We develop the theory of exchange/dipole spin wave excitations of ferromagnetic nanowires of cylindrical cross section, where the magnetization is parallel to the axis of the wire. In addition, we provide the theory of the microwave response of such structures, for the case where the nanowire is also a conductor.…”