Domain-Wall Mobility in Rare-Earth Orthoferrites by Direct Stroboscopic Observation of Moving Domain Walls

Measurements of the temperature dependence of domain-wall mobility in single-crystal plates of Y, Eu, Ho, Er, Tm, and Lu orthoferrites are given in the range from 77°–350°K. Room-temperature values of mobility for all of these orthoferrites fall in the range from 100–1000 cm-sec−1 Oe−1. However, substantial differences in the temperature dependence of the mobility are noted among them. In EuFeO3, the mobility increases from 300 cm-sec−1 Oe−1 at 350°K to almost 3000 cm-sec−1 Oe−1 at 78°K while in HoFeO3 it falls from 230 cm-sec−1 Oe−1 at 350°K to 17 cm-sec−1 Oe−1 at 100°K. Wall mobility is measured using direct stroboscopic observation of a single domain wall whose equilibrium position is modulated by a sinusoidal drive field. Both magnitude and phase of the wall displacement can be measured as a function of frequency. The domain wall is observed by means of the Faraday effect and strobing is achieved with a He–Ne laser beam gated on for a small fraction of the drive cycle by an electro-optic light modulator. The wall mobility is determined from the frequency response of the wall motion which, for these orthoferrites, exhibits a simple relaxation arising from viscous damping.