Magnetooptic color effects in bismuth garnet domains

Domains in magnetic materials having a dispersive Faraday coefficient appear in various colors when viewed by the Faraday effect. If the polarizer and analyzer are slightly uncrossed, domains appear in four colors, three spectral colors and black, depending on the local normal component of magnetization. A theory is presented for this effect. Experimental values of color observed in bismuth substituted garnet films as a function of normal applied field agree with the theory. This effect permits one to discern the average normal component of magnetization at a spot on a micrograph from the color at, that location. Besides the usual bubbles and stripes, unusual domains such as bubble spikes and diamonds and stripe arrays in which the normal component of the magnetization does not change sign are reported.