Condensed Matter Seminar

Dynamics of magnetic vortices in patterned ferromagnets

Dr. Kristen Buchanan
Center for Nanoscale Materials
Argonne National Laboratory

Friday, October 5, 2007 - 4:00 P.M., NSH 184

Nanomagnets have great potential for technologies such as magnetic storage media, magnetic sensors, biomedicine and spintronics and dynamic processes, interesting in themselves, will be an important consideration in device design. Confinement in nanomagnets alters their energetics and leads to new magnetic states, for example, magnetic vortices, which provide a convenient model system for studying fundamental dynamical phenomena. A single vortex in restricted geometry possesses a characteristic translational excitation mode in the sub-GHz frequency range that corresponds to spiral-like motion of the vortex core around its equilibrium position. I will discuss our investigations of the dynamics of magnetic vortices confined in lithographically defined, micron-sized Permalloy disks with circular and elliptical symmetry. The resonance frequencies are detected experimentally using a microwave reflection technique where an r.f. current in a coplanar waveguide generates an oscillating magnetic field that is absorbed preferentially at the eigenfrequencies of the magnetic disks patterned on its central strip.  We have used this technique, combined with micromagnetic simulations, to explore how the frequency the vortex translational mode can be tuned through choice of geometry and static magnetic field, to understand the dynamic interactions of a vortex pair [1], and, more recently, to investigate the effects of increasing the amplitude of the r.f. driving field, where we find that the translational-mode peak in the impedance spectra splits into two well-defined peaks.

This work was supported by the U. S. Department of Energy, Office of Science, Office of Basic Energy Sciences, under Contract No. DE-AC02-06CH11357.

[2] K. S. Buchanan, P. E. Roy, M. Grimsditch, F. Y. Fradin, K. Yu. Guslienko, S. D. Bader, and V. Novosad,  Nature Physics 1, 172-176 (2005).