An exchange-coupled thin-film memory device

A three-layer device is proposed which uses temperature-dependent exchange coupling between two magnetic layers. One layer is composed of a magnetically "hard" material, the other is uniaxial Permalloy. The coupling layer is an alloy that has a Curie temperature near room temperature. A brief pulse of heat applied by means of an optical or electron beam can raise the temperature of the device above its lowest Curie temperature, and the film will change its magnetic state under the influence of an external bias field. An energy calculation for the single-domain case leads to a family of critical curves with exchange coupling as a parameter. An alloy of Ni-Fe-Cr is proposed for use in the coupling layer. Measurements of saturation magnetization versus temperature are reported for sputtered films of the alloy. Although the desired properties are observed for some samples, the alloy appears to be metallurgically unstable.