Pierre E. Roy

Vortex dynamics in patterned ferromagnetic ellipses

The dynamics of individual magnetic vortices and vortex pairs confined in lithographically defined ferromagnetic ellipses were measured using a microwave reflection technique. Resonance frequencies were detected in the subgigahertz range for Ni80Fe20 (Permalloy) ellipses ranging in size from 3 by 1.5μm to 1 by 0.5μm, 40nm in thickness. Micromagnetic simulations indicate that the single mode observed for one vortex is a translational mode and that the two eigenmodes associated with a vortex pair correspond to coupled translational modes of vortices with parallel or antiparallel core polarizations. The single-vortex resonance scales inversely with the ellipse size, in agreement with the simulations and analytical theory.

Magnetic vortex dynamics in elliptical dots: Field dependence and interaction effects

This study aims to investigate experimentally the dynamics of magnetic vortices and vortex pairs confined in lithographically defined Permalloy ellipses using microwave reflection technique. The single vortex magnetization state exhibits a single, low frequency peak in the impedance derivative spectrum for a given external field. Experimental results show that vortex polarization dominates the vortex dynamics while it plays a negligible role in the static interaction.

Deterministic and finite temperature micromagnetics of nanoscale structures: A simulation study

Zero and finite temperature micromagnetic studies have been performed for two nanoscale structures of different geometries by means of numerical integration of the deterministic and stochastic Landau-Lifshitz-Gilbert equations of motion. The results indicate that not only do thermal fluctuations cause a decrease of the coercivity and the time scales involved in switching, but they can also alter the magnetization reversal path. In the case of thermally induced changes in the switching path it is found that with sufficient thermal energy the particle can form other states prior to switching than in the deterministic model. This leads to the identification of two switching regimes in the structures considered, whereby switching from one of the states significantly decreases the coercivity. Furthermore, a study of the time scales involved and the transient magnetic configurations appearing during fast switching was performed.