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

摘要

A magnetic vortex in a ferromagnet with restricted geometry possesses a characteristic translational excitation mode that corresponds to spiral-like motion of the vortex core around its equilibrium position. Elliptical nanodots can take on a either a single vortex or a vortex pair magnetization state, providing a convenient model system for investigating the effects of vortex interactions on their dynamics. Experimentally we have investigated the dynamics of magnetic vortices and vortex pairs [1] confined in lithographically defined Permalloy ellipses using a microwave reflection technique [2]. An r.f. current in a coplanar waveguide (CPW) generates an oscillating magnetic field that is absorbed preferentially when the frequency coincides with a resonance of the magnetic dots patterned on its central strip. Elliptical dots with in-plane dimensions of 2×1μm and 3 by 1.5μm, both of 40-nm thick Permalloy (Py), were patterned directly on top of the waveguides using high-resolution electron beam lithography. The single or vortex pair state can be selected by saturating the sample along the short or long axes, respectively, as confirmed by magnetic force microscopy (Fig. 1).