Spin excitations in vortex-state magnetic dots and rings: from nanometric to micrometric size -- Presentazione orale by R. Zivieri - Conferenza internazionale

An analytical model able to calculate frequencies of surface spin modes in vortex-state ferromagnetic cylindrical dots at zero applied field is formulated. In dots of nanometric radius, the radial eigenvectors of the nonaxially symmetric modes are Bessel functions of order one or greater than one, while the axially symmetric modes correspond to zero order Bessel functions. Instead, in dots of radius R in the micrometric range the radial eigenvectors of the whole set of modes are Bessel functions of order one [1]. The calculated frequencies are compared to experimental data for Permalloy (Py) disks. A deviation of the frequency dispersion from the linear dependence from (L/R)^1/2 where L is the thickness is demonstrated in dots of moderate aspect ratio L/R. Furthermore, the 3D dipolar contribution is calculated exactly and its effect on the spin modes frequencies is discussed. The results are compared with the ones of a micromagnetic approach. The study is extended to ferromagnetic rings in the vortex-state. The effect of the core removal on the spin modes is discussed and the results of the analytical model are compared with those obtained by means of micromagnetic calculations in rings [2]. References [1] R. Zivieri and F. Nizzoli, submitted to Phys. Rev. B [2] G. Gubbiotti, M. Madami, S. Tacchi, G. Carlotti, H. Tanigawa, T. Ono, L. Giovannini, F. Montoncello and F. Nizzoli, Phys. Rev. Lett. 97 247203 (2006); Phys. Rev. Lett. 100 019905 (E) (2008) -- Presentazione orale by R. Zivieri - Conferenza internazional