GB1089817A - A thin magnetic film store and a method of operating such a store - Google Patents

Abstract

1,089,817. Magnetic storage devices. INTERNATIONAL BUSINESS MACHINES CORPORATION. Oct. 7, 1966 [Nov. 2, 1965], No. 44809/66. Heading H1T. [Also in Division H3] A data storage device consists of two thin magnetic films having parallel easy axes and different critical switching fields, and means for applying a biasing magnetic field to rotate the magnetization of one film towards the hard axis without substantially rotating the magnetization of the other film. In Fig. 1 the storage film 12 has a critical field H KS of 5À0 oersted and the switching film 14 has a critical field H KL of 0À5 oersted. The films are evaporated on to a non-magnetic substrate and are separated by a layer 13 of SiO 2 . The biasing field, which may be supplied by a conductor parallel to the easy axis, by a coil or by a permanent magnet, may be applied continuously or only prior to and during a read operation. For read-out if the biasing field is equal to H KL , an equal and opposite field of 0À5 oersted is applied by passing current through a word line, allowing the magnetization of the switching film to fall back to the easy axis in a direction determined by the direction of magnetization of the storage film. The polarity of the output voltage induced in a sense line parallel to the hard axis indicates the data stored. For writing, a word field equal to or greater than the sum of H KS and the biasing field is applied simultaneously with a bit field parallel to the easy axis, so that the magnetization of the storage film is switched. The bit field preferably terminates, and may start, later than the word field. A matrix is described (Fig. 5, not shown) having either separate or common bitsense lines.