Abstract

A method for coupling liquid crystals and a magnetic field to monitor changes in local magnetic properties (e.g., direction of magnetization) is provided. A magneto-optical sensor is used to detect and observe inhomogenieties, impurity phases, of a high energy magnet by monitoring the response of liquid crystals to a magnetic and/or electric field applied perpendicular or antiparallel to the magnetic field supplied by the magnet. The intensity of field necessary to cause a rotation of the liquid crystals in the direction of the applied field, and hence a modification of the optical properties of the liquid crystals, can be used as a rapid, inexpensive quality control test for batch magnet fabrication. The method can be applied to both thin films and bulk specimens. The magnetically weak spots of the sample can be mapped out by noting the appearance of dark and light regions as the liquid crystals are rotated into positions which obscure the illuminating light. Pleochroic dyes, which are long, cylindrically-shaped molecules containing chromophoric groups, can be used to increase the contrast and thus sensitivity of the method since the angle formed between the path of illuminating light and the axis of the pleochroic material determines the color reflected.