Measuring spectrum of spin wave using vortex dynamics

We propose to measure the spectrum of magnetic excitation in magnetic materials using the motion of a vortex lattice driven by both ac and dc currents in superconductors. When the motion of a vortex lattice is resonant with the oscillation of magnetic moments, the voltage decreases at a given current. From transport measurement, one can obtain the frequency of the magnetic excitation with the wave number determined by the vortex-lattice constant. By changing the lattice constant through applied magnetic fields, one can obtain the spectrum of the magnetic excitation up to a wave vector of order 10nm ^-1.