A simple method is described for measuring wall mobility in materials which support cylindrical domains. The mobility is determined from the initial velocity with which a domain wall responds to a field step. A sample, which is demagnetized into the stripe domain state, is subjected repetitively to a fast rise-time pulsed field. The displacement of the stripe domain walls is observed optically as the domains adjust to the new equilibrium configuration. In the particular case of viscous damping and negligible wall mass, for a field step H0 which results in an equilibrium displacement x0, the instantaneous displacement is x=x0[1-exp(-ωct)], where ωc is the ratio of the restoring force constant to the damping constant. The mobility μ=x0ωc/H0. The time-dependent displacement can be displayed graphically in a few minutes by a sampling technique. Measurements on TmFeO3 yield results in good agreement with previous data. The mobility for DyFeO3 is found to be 330 cm (sec Oe)−1.
The effect on the state of polarization of light incident nonnormally onto KDP in the biaxial state is described. The retardation and preferred planes of vibration are calculated as functions of the incident angles. These results are applied to an optical system where the KDP is used as a polarization rotator. The intensity of the light emerging from the optical system indicates the angular limits of the crystal. The computed results are compared with experimentally measured values.
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