Patent GB-1241235-A (GB)
Title: Improvements in or relating to magnetic single wall domain devices
Inventor: BOBECK ANDREW HENRY
IPC: D01G21/00
Filed: 1969-05-01
Abstract: 1,241,235. Magnetic storage devices. WESTERN ELECTRIC CO. Inc. 1 May, 1969 [3 May, 1968; 28 May, 1968 (3)], No. 22199/69. Heading H3B. In a single wall magnetic domain device a domain propagation channel is defined by a magnetic material arranged adjacent to the domain supporting magnetic sheet and arranged so as to cause single wall domains to propagate therealong in response to a direction changing magnetic field in the plane of the sheet. The channel defining magnetic material may be permalloy deposited in a series of zig-zag patterns 12 on a sheet of thulium orthoferrite having an easy axis perpendicular to the sheet in which single wall domains are to be moved. Domains are introduced into the channels C1-CN by severing a domain from a large domain 14 defined by a conductor 15 and selectively extended by input conductors I1-IN by energizing conductor 18. In order to move the domain along the channel a rotating transverse magnetic field is applied by means of two sets of orthogonal Helmholtz coils CP1, CP2 arranged in pairs, Fig. 2 (not shown) and in parallel and actuated alternately. The domain D moves to the position of the closest most highly attracting poles, i.e. positive, produced by the applied fields Hd, Hp of the two sets of coils, Figs. 3A-3D and Figs. 5A-5D. The domains may be moved to the left as viewed in Fig. 3C by reversing the direction of the field Hd. A magnetometer may be employed to provide the rotating field. Instead of all the domains moving synchronously in sheet 11 upon the application of the rotating magnetic field by selecting the width W of the permalloy overlay and the amplitude of the magnetic field domains can be made to move along a single one or several or all of the channels. Information is read out by applying an interrogate pulse to conductor 20 to collapse the domains and produce an output in RO1-RON. Binary information is represented by the presence or absence of a domain in the channel. A negative polarity bias field is applied normal to sheet 11 to contract and control the shape of the domains. The overlay 12 may be crenellated, Fig. 6 (not shown) and of different thicknesses and widths. In the embodiment of Fig. 7 (not shown) the channels are in the form of soft magnetic discs alternate one of the discs being on one surface of the sheet 11 and the other discs being on the opposite surface. A permalloy guide spaced apart from the discs is provided on one surface to form a flux closure for flux in a domain wall encompassing a domain. A Helmholtz coil arrangement is adapted to provide fields consecutively at 90 degrees to one another or a magnetometer may be used to provide continuously rotating fields. The propagation channels may be formed by a magnetic overlay having a generally zig-zag pattern, Fig. 11A and Fig. 10 (not shown) with a conductor 13 aligned with the axis of the pattern and positioned between the overlay and sheet 11. When a current flows in the conductor 13 negative and positive poles are generated in the overlay as shown. A domain introduced at the left moves upwards towards the negative poles to the stable curved area of the overlay. When the current in the conductor is reversed so that the pole distribution is reversed the domain D moves downwards to the next curved stable position to the right. Thus alternate positive and negative pulses permit the domains to move along the channel. Directionality in domain movement can be determined by using a directional magnetic field aligned with conductor 13. By using sets of overlays and conductors at right angles domain movement can be along either of two mutually perpendicular directions, Fig. 13 (not shown). In a further arrangement the channels may be defined by rectangular thin films disposed at angles of 60 degrees with respect to each other, Fig. 15A and Fig. 14 (not shown). A counter clockwise rotating magnetic field causes the domain to move to the right. The magnetic overlay may be in the form shown in Fig. 17A. When a transverse field rotates clockwise to consecutive orientations at 90 degrees with respect to one another a domain moves to the right. A plurality of channels may be connected together to provide recirculating channels. The permalloy pattern may be zig-zag with a closed loop associated with the pattern, Fig. 19 (not shown).