Patent GB-1373298-A (GB)
Title: Magnetic device comprising domains
IPC: G11C11/14
Filed: 1972-07-31
Abstract: 1373298 Magnetic and magneto-optic storage devices; electro-acoustic transducers PHILIPS ELECTRONIC & ASSOCIATED INDUSTRIES Ltd 31 July 1972 [3 Aug 1971] 35650/72 Headings H3B and H4J [Also in Division G1] Motion of single wall domains in a first magnetic sheet is controlled by the motion or position of single wall domains in a second, adjacent sheet. The field of a domain in the controlling sheet interacts with that of a domain in the first sheet to provide a preferred site for it. If the controlling sheet 52 is filled with fixed position domains 54, Fig. 5a, this provides preferred sites in sheet 51 between which the information representative domains 53 of a storage device may be moved by conventional means; if the domains in the control sheet are movable, as are domains 64, Fig. 6a, by conductor loops 66, 67, the information representative domains 63 in the adjacent sheet will also be moved by the conductor loops. One control sheet may be used with several information carrying sheets, Fig. 4b (not shown). In another embodiment, Fig. 13 (not shown), the plates are periodically moved closer and further apart; this varies the domain size, and can be used to propagate the domains in the first sheet along an angel fish overlay. The interaction between domains may be sufficient to render an external bias field unnecessary. Hollow (annular) and strip domains may be used. Logic.-The control sheet may also be used in a logic device, with the control domains serving to attract or deflect domains in the first sheet along a desired path. In Fig. 9, for example, a domain 83 propagating in the first sheet 81 under the influence of T-bar overlays will emerge at output a.b if a domain 84 (shown dotted) is present in an adjacent control sheet, but will emerge at output a.b if domain 84 is absent. Likewise in Fig. 10 (not shown) a control domain determines which path is taken where an angel fish overlay branches. Optical reading.-Because of the interaction forces between the sheets if domains are established in the control sheet then domains in the first sheet will position themselves above the control domains, in effect copying the control sheet. This can be used to enhance optical reading, since the crystal orientation of the control plate may be an optimum for displacing domains, while the crystal orientation of the first sheet is selected for the best optical reading by, e.g., the Faraday effect. Displacement and acoustic transducers.-Fig. 12 shows two adjacent sheets 111, 112 containing single wall domains 113, 114. The dimensions of these domains are determined by the magnitude of the magnetic field each imposes on the other. When the spacing between the sheets increases, the domain diameters thus increase, and the resulting flux change cause an electrical signal in conductor loop 117. Thus the signal depends on the separation change between the plates; this may be used to convert acoustic vibrations to an electric signal, or to measure the separation change. The conductor loop 117 may be replaced by a magnetostrictive permalloy foil near domain 114. By passing a current through the conductor loop the plate separation is controlled, and thus an electric signal can be converted to acoustic vibrations.