Spin-wave discretization in cylindrical permalloy dots -- Presentazione orale by R. Zivieri - Conferenza internazionale

A detailed investigation of the dynamical magnetic properties of arrays of permalloy disks with radius between 0.1 and 0.5 micron and fixed thickness of 50 nm is presented. The arrays of dots were fabricated using electron beam lithography and lift-off technique. The Kerr hysteresis loops measured in the longitudinal configuration showed that the magnetic vortex state [1] is the ground state of the dots with annihilation and nucleation fields which depend on the dot radius. Brillouin Light Scattering experiments from spin waves, exploited in the saturated state, gave evidence of a marked discretization of the spin wave spectrum with respect to that of the continuous Permalloy film. The dependence of the frequency of the discrete modes on both the intensity of the external applied field and the in-plane wave-vector has been measured. The modes observed at high frequencies are discrete surface magnetostatic waves. The modes at low frequencies are identified as bulk backward magnetostatic spin waves and tend to disappear in the Brillouin spectra with increasing the disk radius. A considerable agreement between the measured frequencies and the calculated ones according to the Guslienko-Slavin model has been obtained for the high frequency modes. The low frequency modes have been interpreted in the framework of the formalism of the backward volume modes applied to disks [2]. [1] T. Shinjo, T. Okuno, R. Hassdorf, K. Shigeto, and T. Ono, Science vol. 289, 930 (2000). T. Okuno, K. Shigeto, T. Ono, K. Mibu, and T. Shinjo, J.Magn. Magn. Mater . 240, 1 (2002) [2] G. Gubbiotti, G. Carlotti, R. Zivieri, F. Nizzoli, T. Okuno and T. Shinjo, J. Appl. Phys., to be published -- Presentazione orale by R. Zivieri - Conferenza internazional