The basic magnetic properties of three-dimensional nanostructured materials can be drastically different from those of a continuous film. High-resolution magnetic force microscopy studies of magnetic submicrometer-sized cobalt dots with geometrical dimensions comparable to the width of magnetic domains reveal a variety of intricate domain patterns controlled by the details of the dot geometry. By changing the thickness of the dots, the width of the geometrically constrained magnetic domains can be tuned. Concentric rings and spirals with vortex configurations have been stabilized, with particular incidence in the magnetization reversal process as observed in the ensemble-averaged hysteresis loops.

We report on the observation of quantized surface spin waves in periodic arrays of magnetic Ni 81 Fe 19 wires by means of Brillouin light scattering spectroscopy. At small wavevectors (q || ≅ 0 -0.9·10 5 cm -1 ) several discrete, dispersionless modes with a frequency splitting of up to 0.9 GHz were observed for the wavevector oriented perpendicular to the wires. From the frequencies of the modes and the wavevector interval, where each mode is observed, the modes are identified as dipole-exchange surface spin wave modes of the film with quantized wavevector values determined by the boundary conditions at the lateral edges of the wires. With increasing wavevector the separation of the modes becomes smaller, and the frequencies of the discrete modes converge to the dispersion of the dipole-exchange surface mode of a continuous film.Patterned magnetic films are attracting increasing interest due to their potential applications in magnetic storage devices and sensors. Although static properties and coupling phenomena in magnetic films patterned on the micron scale have been studied extensively [1,2,3,4], high-frequency dynamic properties of such films have been rarely investigated. On the other hand, the study of spin wave properties in conventional finite size systems is well established, such as the investigation of so-called Walker-modes in magnetic spheroids [5], and of dipolar-dominated surface modes (Damon-Eshbach modes) in finite-thickness slabs with infinite lateral dimensions [6]. For periodic, micron-sized magnetic structures such a study has been still lacking, likely due to the high requirements both concerning the sample quality and the performance of the Brillouin light scattering experiment to detect the rather weak spin wave signals. In this Letter we report on the observation of quantization of spin waves in an array of magnetic wires. The quantization effects are identified as being due to the finite width of the wires. The evolution of the Damon-Eshbach mode of a continuous film from the discrete eigenmode spectrum of the wires with increasing wavevector, i.e., with diminishing influence of the finite size effect, is demonstrated and quantitatively described by a model based on quantized dipoleexchange modes. We show that both the frequency values and the wavevector intervals, where these modes are observed, are in a good agreement with our proposed model. The samples are made of a 200 Å thick permalloy (Ni 81 Fe 19 ) film deposited in UHV onto a Si(111) substrate by means of e-beam evaporation. Patterning was performed using X-ray lithography. The patterning masks were fabricated by means of a JEOL 5D2U nanopattern generator at 50 keV. X-ray exposure was performed at the super-ACO facility (LURE, Orsay, France) using a negative resist with a lift-off process with Al coating and ion milling. Two samples with periodic arrays of wires with a wire width w=1.8 µm and distances between the centers of the wires, Λ, of 2.5 µm and 4 µm (i.e., wire separations of 0.7 µm and 2.2 µm) were prepared for the inv...

An experimental study of spin-wave quantization in arrays of micron-size magnetic Ni 80 Fe 20 wires by means of Brillouin light-scattering spectroscopy is reported. Dipolar-dominated Damon-Eshbach spin-wave modes laterally quantized in a single wire with quantized wave vector values determined by the width of the wire are studied. The frequency splitting between quantized modes, which decreases with increasing mode number, depends on the wire sizes and is up to 1.5 GHz. The transferred wave vector interval, where each mode is observed, is calculated using a light-scattering theory for confined geometries. The frequencies of the modes are calculated, taking into account finite-size effects. The results of the calculations are in a good agreement with the experimental data.