A system for measurement of domain wall motion in amorphous rare earth-transition metal alloys

A system has been developed for measuring domain-wall motion in amorphous rare-earth-transition-metal alloys. A one-dimensional scanning technique is utilized in which a focused, oscillating HeNe laser spot moves over the magnetization pattern in the film. Domain walls are detected through the polar Kerr effect as the spot scans the film. A magnetic field is applied to the film in order to move the domain walls. The maximum line-scanning rate is about 250 Hz. The spot diameter at a 632.8-nm wavelength is limited to about 8 μm by the 0.46 numerical aperture of the focusing objective, the beam waist of the laser, and aberrations. The domain wall position can be measured to within ±1 μm. The apparatus is described, and the results domain-wall-motion measurements are presented