Patent GB-1438049-A (GB)
Title: Magnetic domain systems using domains having different properties
IPC: G11C11/14
Filed: 1974-05-23
Abstract: 1438049 Magnetic storage arrangements INTERNATIONAL BUSINESS MACHINES CORP 23 May 1974 [29 June 1973] 23032/74 Heading H3B It is shown that a magnetic bubble may have a plurality of vertical bloch lines within its domain wall and that the number of bloch lines present may be utilized to represent information, bubbles of like character being distinguishable by the angle through which they move with respect to a propagating gradient magnetic field. Examples of such bubbles are shown in Fig. 3 which includes a rotation identifying bubbles 12A to 12D of different character in terms of the positive or negative sense of rotation around the domain wall of sequential bloch lines, the number of bloch lines, and the number of revolutions of the internal wall magnetization along its perimeter. Only the magnetic bubble 12B characterized by - 2 bloch lines and 0 wall magnetization rotations moves in the direction of a magnetic gradient field H Z1 , H Z2 , Fig. 4A, other bubbles being deflected by an angle # in accordance with their respective positive or negative rotational sense and the number of revolutions of the internal wall magnetization. Bubble generation.-A suitable magnetic bubble containing vertical bloch lines is developed by splitting off from a stripe domain 44, Fig. 6A, a domain splitting field being applied by a current loop 46 so as to produce a magnetic field at point A different from that existing at point B. The duration T of a current pulse I in the loop 46 determines the number of bloch lines in the generated bubble. Propagation of the split-off bubble in direction 50 along an overlay pattern of T and I bars is then effected by a rotating in-plane field H. The remainder of the split domain can be elongated to a stripe for further bubble generation by lowering the bias field H Z . In a modification, Fig. 6B, the stripe domain 64 is created by a current loop 56 and splitting with bloch wall generation is effected by current loop 46 as in Fig. 6A. An alternative arrangement, Fig. 6C, uses a permalloy disc 68 about which a domain is continuously rotated by an in-plane field H. The rotating domain is elongated by an I-bar 76 and splitting by current in a loop 74 is then effected as previously described. In Fig. 6D a domain 82 is elongated at an expansion position 80 in a domain propagation path 70 of T- and I- bars, splitting being effected by a current loop 84. Domains are continuously generated by splitting from a magnetically soft disc, and are selectively propagated to the expansion position by passing an annihilation loop 88 connected to a controlling current source 90. Other methods of generating bubbles having vertical bloch walls include a gradient magnetic field produced across a stripe domain by adjacent magnetically soft material in combination with the rotating in-plane field, or the bringing of another magnetic domain into the vicinity. Domains with randomly generated numbers of vertical bloch walls may also be generated, which are then separated according to their character by their direction of propagation in a gradient magnetic field, Fig. 7. Reading.-Mixed bubbles propagated along a path 136, Fig. 9, are separated into their characteristic types by a gradient magnetic field H Z1 , H Z2 , and pass along respective propagation paths 138 to magneto resistive detectors 146A-146C in staggered connection to provide sequential readout. Bubble sorting and storage.-Bubbles from a generator 94, Fig. 7, are separated according to the number of vertical bloch lines and positive or negative revolution by a gradient magnetic field 100 produced between parallel pulsed conductors 102A, 102B. Bubbles characterized by + 1, 0 and - 1 rotations are directed by the gradient field to respective propagation paths leading to +1, 0 and - 1 circulating storage bins, while bubbles of higher rotational order are angularly deflected to such an extent that they are absorbed by annihilators 122. The domains entering respective bins are counted by counters 112-0, 112-1, 112+1 which apply domain collapse currents to loops 114-0, 114-1, 114+1 when an associated bin is full. Domains stored in a circulating bin may be passed to a storage or logic input over a propagation path 120 by operating a switch SW0, SW+ 1, SW - 1, Fig. 8 (not shown).