Patent GB-896703-A (GB)
Title: Improvements in or relating to bi-stable magnetic elements and devices incorporatingsuch elements
Inventor: WILLIAMS MICHAEL
IPC: H03K17/84
Filed: 1959-08-07
Abstract: 896,703. Magnetic storage devices. GENERAL ELECTRIC CO. Ltd. Aug. 8, 1960 [Aug. 7, 1959], No. 27092/59. Class 38 (2). [Also in Group XXXIX] A thin magnetic film is set to one stable remanent state A, Fig. 2, along its easy axis of magnetization by a pulse producing a crossfield C inclined out of the perpendicular to the easy axis, and is set to the other state B by the simultaneous application of the cross-field pulse and a writing pulse which develops a writing field S lying approximately along the easy axis in the direction of the other remanent state B, the cross-field pulse being terminated before the writing pulse. A film of ferromagnetic material such as 80% nickel, 20% iron having a maximum thickness of about 3000 angstrom units is used, and is deposited on a fire-polished glass sheet or a sheet of polished aluminium. The cross-field C has a magnitude exceeding the saturation field of the film and has a component OD along the easy axis, e.g. of about 10% of the saturation field, sufficient to set the magnetization to state A when the cross-field is removed. The writing field S on the other hand produces a component OE along the easy axis in the opposite direction and of just over twice the value of component OD, the writing field being below the saturation value. To set the film into state A the cross-field pulse alone is applied, the magnetization state being obtained when the pulse is terminated. To set the film to state B the writing pulse is applied slightly delayed with respect to the cross-field pulse. As the writing pulse field component exceeds the cross-field component along the easy axis and acts in the opposite sense, the magnetization is set to state B when the cross-field pulse and then the writing pulse are sequentially terminated. The films may be employed in a storage matrix and may be deposited on a common substrate at the crossing-points of strip row and column conductors S1-S4, C1-C400, Fig. 1. Each film F has its easy axis of magnetization slightly inclined to the column conductors and a separate read-out conductor P1-P4 is provided for each row. Setting of a film to state B is effected by coincidently pulsing a selected row and a column conductor from pulse generators CPG, SPG, the writing pulse in the selected row having no effect on other films in the row since its magnitude is appreciably less than the saturation field. Reading of a selected column of films is carried out by energizing that particular column with a cross-field pulse from a generator CPG. A film in state A is switched from A to saturation direction C and back to A at the end of the pulse, thus inducing two successive output pulses of opposite polarities in the associated read-out conductor. A film in state B is changed to state A via saturation C, and two output pulses are produced which are both of the same polarity. Discrimination is effected by gates G1-G4 which pass only the first of the two output pulses, the magnetization state of the film being then represented by the output pulse polarity. Constructional details are outlined including the use of several glass sheets each bearing a number of films to form the matrix, both sides of the sheet being overlaid by stacked printed circuit-boards carrying the various conductors. Specification 890,754 is referred to.