MEASUREMENT OF SMALL DISTANCES BETWEEN LIGHT SPOTS BY DOMAIN-WALL DISPLACEMENTS

Two laser beams are focused onto a thin permalloy film. By changing th e direction of the magnetization of the permalloy film, the Kerr effec t is exploited to either rotate the plane of polarization or modulate the amplitude of the reflected light. First, the film is characterized for our application by measuring the velocity of the domain wall disp lacements by two focused beams with known distances. By measuring the delay between the modulation of the reflected beams, it is possible to accurately determine the beam separation under the condition of repro ducible wall movements. Therefore, a moving domain wall acts like a hi gh-speed modulator. The method could be used for many applications, e. g., refraction measurements or rapid quality control of magnetic mater ials.