Patent GB-1224495-A (GB)
Title: Thin film magnetic information stores
Inventor: VALIN JEAN
IPC: G11C13/06
Filed: 1968-03-22
Abstract: 1,224,495. Magnetic storage arrangements. COMPAGNIE INTERNATIONALE POUR L'INFORMATIQUE, and CENTRE NATIONAL DE LA RECHERCHE SCIENTIFIQUE. 22 March, 1968 [29 March, 1967], No. 14072/68. Heading H3B. [Also in Division H1] A magnetic storage structure comprises a layer of anisotropic ferromagnetic material magnetically coupled to a layer of an antiferromagnetic material. The antiferromagnetic material has its domains immediately adjacent the ferromagnetic material in such a direction as to lock its magnetic storage state, and so enables non-destructive read-out to be effected. The existing magnetic state may be changed by heating the antiferromagnetic material to above its temperature of atomic disorder (the Neel temperature) and applying a magnetic field in the required direction during the cooling process. An alternating magnetic field applying during cooling erases the information stored without writing new information. Suitable materials for the structure are stated to be cobalt or nickeliron (80%-20%), for the ferromagnetic material, and cobalt oxide, chromium oxide, or nickel-iron-manganese for the antiferromagnetic material. As shown in Fig. 4, the structure comprises adjacent thin layers of antiferromagnetic material 1 and ferromagnetic material 2 on a glass substrate 3, the metallic layers being either in contact, as shown, or separated by a thin layer of non-magnetic material, Fig. 3 (not shown). A second layer of ferromagnetic material 5 separated from the first layer 2 by a thin gold layer is optional. The structure is formed by deposition processes in the presence of a magnetic field, and in the case of a structure using nickel-iron as the anisotropic ferromagnetic material, a coating of manganese may be diffused into the surface of the ferromagnetic material by heat treatment so as to form an integral antiferromagnetic layer of nickel-iron-manganese. A semi-permanent matrix store is formed by a co-ordinate array of parallel conductors glued to the structure, Fig. 9 (not shown), the conductors being formed by selectively etching metallic layers coated on both sides of a thin insulating sheet. Crossing points of the conductors define discrete storage areas which are read out non-destructively by passing current through conductors extending along the easy axis of magnetization of the ferromagnetic material. Alternatively, current may be passed through conductors extending along the hard direction of magnetization at the same time as a hard-direction biasing field is applied. In a modification the conductors may be omitted and the information stored read out as shown in Fig. 12 by a displaceable scanning head comprising a light source 13 and a photo-electric detector 14. The emergent light is polarized at 33, and the light reflected from the portion of the magnetic structure at which it is directed is analysed at 34. Scanning by a displaceable head can be avoided by providing a mosaic of photoelectric detectors, one for each storage location, and either scanning with a polarized light beam or lighting the whole surface of the structure with polarized light. The stored information may be changed by using a heat source 20, Fig. 13, such as a ruby laser, to raise the temperature of those areas of the storage structure exposed by coded perforations in a mask 17, an orienting magnetic field for the exposed portions being applied to the storage structure 18. Alternatively a single heating spot may be selectively directed to required locations in a storage structure by moving the structure in two coordinates in accordance with a programme recorded on a magnetic or punched tape, Fig. 15 (not shown). Erasement of information stored without writing new information may be effected by cooling from above the disorder temperature in an alternating field. Read in at selected storage locations is then carried out by localized reheating in the presence of a unidirectional field.