Magneto-optic studies of wall vibration

We describe our magneto-optic domain-wall-oscillation spectrum analyzer and its application to quantitative studies of forced vibrations of various walls in garnet thin films including periodic bubble lattices, periodic stripe patterns, and charged walls with and without an attached bubble. Linear oscillator analysis of the main Bloch wall resonance ν0yields the effective wall mass and viscous damping coefficients. A higher-frequency mode ν2of wall flexure having two nodes is also observed and discussed. Nonlinear phenomena at high drive include saturation of amplitude consistent with Bloch-line nucleation in one range of frequencies including ν0and with the Walker-deLeeuw mechanism in another including ν2. At moderate drives standing wall-vibration waves are excited both directly and parametrically. Waves observed in the space of wave vector, amplitude and frequency using spatial Fourier transform (Fraunhofer) magnetooptics, are discussed in terms of dispersion calculations for the parallel stripe pattern. Oscillations of charged walls and Néel walls were also detected for the first time in thin garnet layers (< 1μm). The large wall width inferred from charged wall mobility may explain an observed absence of velocity saturation up to 280 m/s.