Optimum Thickness of MnBi Films for Magnetooptical Memory

Magnetic behavior of thermomagnetically written domains in MnBi films (400 A to 1200 A thick) has been studied. The written domains were circular in shape but became deformed and irregular with increasing film thickness. The circular domains of 1.5 microm in diameter were stable only in the films thinner than 700 A for writing and erasing processes. The stability of written domains can be explained by introducing measured wall coercivity values into a domain theory. The film wall coercivity was varied from 250 Oe to 800 Oe in inverse proportion to the film thickness.