Inductive detection of magnetic vortex gyration

Vortex cores in Landau-domain patterns are resonantly excitable by alternating magnetic fields in the sub-gigahertz regime. We present a highly sensitive method to detect the vortex gyration in single micrometer-sized elements spectroscopically by measuring spectra of induction voltages caused by the stray fields of a single ferromagnetic square exposed to an alternating Oersted field. A distinct change of the induction voltage is observed around the resonance frequency of the vortex core. The shape of the measured spectra deviates from Lorentzian profiles due to voltages induced by magnetic fringing fields of the exciting currents. An analytical description of the measured spectra is given. A characteristic frequency shift in external magnetic fields proves that signals detected by the induction sensor originate from the dynamically excited Landau-domain pattern. The measurements on a single square are compared with measurements on an ensemble of uniform squares.