Patent GB-1434263-A (GB)
Title: Magnetic domain system
IPC: G11C19/08
Filed: 1973-11-20
Abstract: 1434263 Magnetic storage arrangements INTERNATIONAL BUSINESS MACHINES CORP 20 Nov 1973 [29 Dec 1972] 53700/73 Heading H3B Two types of magnetic bubbles, of which type A is distinctly larger than type B and has a more clearly defined domain wall when viewed by using a Faraday magneto-optical system, are generated and utilized at the same time in a magnetic sheet with a constant magnetic bias. The two bubble types A and B may respectively replace the use of bubble presence and absence to denote binary data. As shown in Fig. 3, magnetic bubbles of both types are generated in a magnetic sheet 10 subjected to a bias field Hz by applying a current pulse to a loop 22 to break up strip domains 36. A further pulse in the same direction will convert type B bubbles to type A, while a pulse in the opposite direction will convert type A bubbles to type B. Generated bubbles are propogated along a T and I bar permalloy pattern 30 by an in-plane rotating magnetic field H. The theoretical characteristics of the type A and B bubbles are shown in Fig. 2A, the type A bubbles being characterized by a substantially uniform diameter through the thickness of the sheet while the type B bubbles are broad only in the waist, Fig. 2A, penetrate only partially through the sheet, Fig. 2B, or are tapered as shown in Fig. 2C. Centres 16 of reversed magnetization may exist. A shift register formed by propagation pattern 40, Fig. 4, has separate generators 38A, 38B which respectively breakup strip domains 46A, 46B into type A and type B bubbles. Propagated bubbles are detected by a sensing circuit 50, 52 which may be magnetoresistive or a tuned oscillatory arrangement as described in Specification 1,372,516, the level of the output signal denoting the type of bubble detected. An alternative register, Fig. 5, using presence and absence of B type bubbles only to increase the packing density, the mixed bubble types split from a domain 46B by a generator 54 being converted uniformly into type A or B type bubbles by application of current of appropriate direction to a loop 56. In addition to the sensing circuit 52, a path changing switch SW for bubble read out is provided, the deflected bubbles being converted from B type to A type at a converter 60 before passing to a sensor 62. In Fig. 6 the bubble domain propogation path is formed by permalloy disco 64 located alternately on opposite surfaces of the magnetic sheet 10, the domains being constrained by a permalloy guide rail 66. Sources 38A, 38B supply A and B type bubbles, respectively. Domains in the propagation path may be collapsed simultaneously by passing current from a source 70 through a loop formed by the guide rail 66 and a conductive non- magnetic strip 68. A similar arrangement, Fig. 7 (not shown) uses a single domain generator. A matrix store for A and B type domains is shown in Fig. 9, the selective application of currents to row and column conductors X1-X4, Y1-Y4 forming A or B type bubbles or the conversion of one type to the other. Optical readout using the Faraday effect is obtained by a beam from a laser 72 which is polarized at 74, scanned at 76, analysed at 78 and detected by a photocell 80. It is stated that the magnetic sheet 10 may store a numeral or character in pattern form which is read out by illuminating with polarized light the whole of the sheet.