SEMINARIUM
Oddziału Fizyki Magnetyków i Zjawisk Kooperatywnych

Dnia: 12.10.2012 roku (piątek)
o godzinie 10:00 w auli Instytutu

referat pt.:

Probing arrays of circular Permalloy microdots with Ferromagnetic resonance

wygłosi

prof. Gleb Kakazei

University of Porto, IFIMUP and IN - Institute of Nanoscience and Nanotechnology, Porto, Portugal

Square arrays of circular Permalloy submicron dots were systematically studied by different ferromagnetic resonance (FMR) techniques. Using continuous-wave FMR spectrometer with precise computer-controlled goniometer, it was found that upon a small inclination of the external magnetic field from the normal, each n-th standing spin-wave mode, except of the strongest one n = 1, splits at some angle into several ones. Number of splitted modes depends on the mode number. This effect was found to be a result of common action of confinement, geometry of dots and breaking of the initial cylindrical symmetry by canted field. Using broadband FMR, it was demonstrated that breaking the cylindrical symmetry of the magnetic vortex gradually changes and suppresses the azimuthal spin eigenmodes below the vortex nucleation field and leads further to the appearance of new eigenmodes. The parallel microwave field pumping was shown to be a unique tool to observe spin excitation modes localized near the strongly shifted vortex core for the bias field between the vortex nucleation and annihilation fields. Meanwhile, the perpendicular field pumping, which excites the spin waves throughout the entire dot, reveals a crossover between two dynamic vortex regimes near the nucleation field. In the absence of external field, a considerable influence of the dot separation on the gyrotropic vortex frequency and splitting of the azimuthal spin wave frequencies was detected. The gyrotropic frequency and the first azimuthal doublet frequency splitting depend nonmonotonously on the dot spacing, whereas the dependence of the second doublet frequency splitting on this parameter is monotonous. The observed effects were explained by the influence of both the dipolar and quadrupolar contributions to the dynamic magnetostatic interactions.