Optical mass memory experiments on thin films of MnBi

Experimental studies of laser Curie-point writing, erasure, and magnetooptical read-out on thin films of MnBi have been performed. These films have a thickness of around 800 Å, an optical density of 1.6, and a Faraday rotation of 5 degrees (0 to full saturation) at a 6328-Å wavelength. Their easy direction of magnetization is normal to the film plane; coercive force Hcis between 800 and 1100 Oe; and Curie temperature Tcis 360°C. These properties make them well suited for optical mass memory applications. This has been demonstrated with a scanning optical system designed to simulate the functions of a computer memory. A 50-mW He-Ne laser beam is modulated with a Kerr cell, deflected with a galvanometer, and focused onto the film with a microscope objective. Memory bits of 1-μm diameter were written, read, and erased through 10⁵cycles with no degradation of its memory characteristics. The experiments were carried out at room temperature in air.