A study has been made of the domain structure of thin films (∼1000 A) of MnBi and their capability of storing information magnetically. It is estimated that a million bits of information could be written on a square centimeter of film. The information can be read out optically by utilizing the Faraday effect. The films have a uniaxial direction of easy magnetization normal to their surfaces and retain their magnetization after saturation along this direction in spite of the large demagnetizing factor. When magnetized in this manner, a high optical contrast is obtained between the writing and the background.