Microwave properties of metallic nanowires

Abstract

We report on the microwave properties of arrays of parallel magnetic nanowires constituted of nickel, cobalt, or Ni/Fe alloy embedded in nanoporous track-etched polymer membranes. The experiments consist of transmission measurements carried out on microwave stripline structures using a magnetically loaded membrane as the substrate. Measurements were performed at frequencies ranging from 100 MHz to 40 GHz and under static magnetic fields up to 5.6 kOe applied along the wires axis. Resonance phenomena have been observed in the magnitude of the complex transmission coefficient at frequencies which depend on the nature of the material and applied static magnetic field. Results are consistent with those expected for a ferromagnetic resonance (FMR) experiment and the observed behaviors are analyzed in the framework of the classical FMR theory.

Ferromagnetic resonance on Ni nanowire arrays

“…The estimated value of the magnetization at saturation is smaller than the value reported for bulk Ni (4pM S 5 6.2 6 0.05 kGauss 8,12 ). This relatively small difference may be due to the deviation from the assumed cylindrical symmetry, to the effect of the uniaxial magnetocrystalline anisotropy, induced by local stresses, and to dipolar interactions among nanowires.…”

“…The effective field is close to the expected value (H eff % 3.0 kOe), typical for a system with g 5 2.21. 12 The estimated value of the magnetization at saturation is significantly lower than the values of the magnetization at saturation for bulk Ni (4pM S 5 6.2 6 0.05 kGauss 8 ) and is to large to be assigned to shape and magnetocrystalline anisotropies 8 or dipolar interactions among nanowires. By fitting the experimental data within the real nanowires approximation, the correlation between the predicted values and the measured ones is slightly improved (see the dotted curve in Fig.…”

“…8,10,17 The perfect nanowire approach preserves the ideal shape of the nanowire (N X 5 N Y 5 N ⊥ 5 2p and N Z 5 N k 5 0) and allows for a local uniaxial magnetocrystalline anisotropy, K A , which is responsible for a local field H A 5 K A /l 0 M S . The free energy of a magnetic nanowire within this approximation is:…”

“…[23][24][25][26][27][28][29][30][31][32][33][34][35] The magnetic properties of Ni nanowires are controlled by the shape anisotropy, to which shape and magnetocrystalline contributions act as small perturbations. The main difference between the ideal nanowire and the real nanowire descriptions consists in the replacement of the cylinder-like symmetry with an ellipsoid of rotation symmetry.…”

Ferromagnetic Nanorings

“…Much progress has been accomplished recently in accessing both the spin-wave modes in conf ned geometries [73][74][75][76][77][78] and in probing the out of equilibrium magnetization dynamics [79][80][81][82][83]. For the specif c case of the ring geometry, ferromagnetic resonance (FMR) [78,84,85], time-resolved MOKE [85] and Brillouin light scattering (BLS) [86] measurements have been performed to probe and determine the spin-wave eigenmodes characteristic of magnetic rings.…”