AVS 50th International Symposium
    Magnetic Interfaces and Nanostructures Thursday Sessions
       Session MI-ThA

Invited Paper MI-ThA5
Real-Time Imaging of Spin Dynamics in Magnetic Vortex Structures

Thursday, November 6, 2003, 3:20 pm, Room 316

Session: Magnetization Dynamics
Presenter: J.P. Park, University of Minnesota
Authors: J.P. Park, University of Minnesota
P. Eames, University of Minnesota
D.M. Engebretson, University of Minnesota
P.A. Crowell, University of Minnesota
Correspondent: Click to Email
Patterned nanometer-scale magnetic structures have been proposed as media for high-density data storage. A prerequisite for implementing such a technology will be an understanding of the fundamental characteristics of magnetic nanostructures, including switching times, damping constants, and the spatial distribution of collective modes. We use time-resolved Kerr microscopy to study the spin dynamics of individual ferromagnetic disks with thicknesses of 50 nm and aspect ratios @beta@= L/R ~ 0.1 - 0.5, where L is the thickness and R the radius.@footnote 1@ The equilibrium state of each disk in zero field is a vortex with a singularity at the center. As the field is reduced from saturation, the vortex nucleates at one edge of the disk, and it moves across the diameter until it is annihilated at the opposite edge in negative fields. We observe three distinct excitations of this vortex state, in contrast to the simple uniform precession observed in the saturated state. The lowest mode corresponds to the gyrotropic motion of the entire vortex around its equilibrium position.@footnote 2@ The exact nature of the higher modes is being explored through a combination of spatially-resolved spectroscopy and micromagnetic simulations. The frequencies of all three vortex modes are nearly independent of the value of the applied field and hence the position of the vortex inside the disk. This work was supported by NSF DMR 99-83777, the Research Corporation, the Alfred P. Sloan Foundation, the University of Minnesota MRSEC (DMR 02-12032), and the Minnesota Supercomputing Institute. @FootnoteText@ @footnote 1@J. P. Park, P. Eames, D. M. Engebretson, J. Berezovsky, and P. A. Crowell, Phys. Rev. B 67, 020403R (2003). @footnote 2@K. Yu. Guslienko et. al., J. Appl. Phys. 91, 8037 (2002). .