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Electron beam lithography has been used to prepare 250-Å-thick square-shaped permalloy dots whose width and separation are in the range between 1 and 4 m. The static and dynamic magnetic properties of these structures have been investigated by complementary techniques such as magneto-optic Kerr effect ͑MOKE͒, magnetic force microscopy ͑MFM͒, and Brillouin light scattering ͑BLS͒. Longitudinal MOKE enabled us to compare the hysteresis loops of the specimens with different dot size and interdot separation, showing a marked influence of the demagnetizing field inside the dots. MFM images recorded at zero applied field showed that, depending on the interdot spacing, there is a prevalence of either four-or seven-domain patterns together with a minority of nonsolenoidal patterns that possess a net magnetic moment. BLS from thermally activated spin waves were then used to determine the intrinsic magnetic parameters of the permalloy films and to show evidence of the discretization of the spin-wave peak due to the wave vector resonance condition within each dot.

We present the results of a study of the magnetization reversal in Permalloy triangular rings using diffracted magneto-optics Kerr effect combined with numerical micromagnetic simulations and in-field magnetic force microscopy. Diffracted loops show a two-step switching process for external fields along or perpendicular to any of the ring edges. The diffracted loops calculated from micromagnetic simulations reproduce the measured ones and show that the switching occurs from one asymmetric onion state to the reversed state, for both directions of the applied field. In both cases a stable intermediate vortex state appears during the switching, accounting for the diffracted loop structures. The stability and the magnetization chirality of the vortex state depend on the direction of the applied field relative to the ring orientation. Magnetization configurations occurring during reversal imaged with magnetic force microscopy operated applying an external field confirm the above reversal process.

Magnetometric and magnetic force microscopy (MFM) measurements were performed on [Co(6 Å)/Au(27 Å)]27 multilayers grown at different sputtering pressures (0.8–9 Pa). All the as-prepared samples display perpendicular magnetic anisotropy that has its maximum value at intermediate pressures, while a monotonic decrease of the saturation magnetization was found with increasing pressure. As found by MFM, a relevant characteristic of these systems is the magnetic stripe domain structure. The application of the stripe domain model of Draaisma and de Jonge [H. J. G. Draaisma and W. J. M. de Jonge, J. Appl. Phys. 62, 3318 (1987)] allows us to satisfactorily reproduce the magnetization processes and to determine the anisotropy constants (Keff) starting from the domain width. The obtained Keff values display the same behavior and order of magnitude as those deduced from the area enclosed between parallel and perpendicular magnetization curves. The measurement of the stripe domain size with MFM thus results in an easy and reliable method for the evaluation of the anisotropy constants in multilayers with perpendicular anisotropy.