Probing vortex-core dynamics using current-induced resonant excitation of a trapped domain wall

Magnetic domain walls in soft magnetic nanowires often exhibit a structure in which the magnetization curls within the plane of the nanowire around a singular point with out-of-plane magnetization, the vortex core(1,2). Although the core is a small object, with a diameter of only similar to 10nm in permalloy(2), its motion controls the dynamics of the entire wall, which can be several hundred nanometres in size. In particular, when a domain wall trapped at a pinning site is driven out of equilibrium by either a magnetic field or a spin-polarized current, the vortex core gyrates around its equilibrium position. The sense of gyration is determined by the polarity of the core(3-7). Here, we show that spin-polarized a.c. currents can resonantly excite a vortex domain wall trapped at a notched site in a nanowire. The shape and magnitude of the resonance, measured from the nanowire's resistance, reveal both the elliptical trajectory of the vortex core as well as its polarity.