Patent GB-1021556-A (GB)
Title: Method and apparatus for information storage with thin magnetic films
IPC: G11C11/15
Filed: 1963-07-24
Abstract: 1,021,556. Circuits employing magnetic storage elements. MAX-PLANCK-GESELLSCHAFT ZUR FORDERUNG DER WISSENSCHAFTEN E.V. July 24, 1963 [July 24, 1962; March 15, 1963 (2)], No. 29391/63. Heading H3B. [Also in Division H1] Magnetic elements of a binary storage element comprise thin magnetic films having easy and hard axes of magnetization and conductors adjacent the films for applying magnetic fields to them, binary information being stored in the films by magnetization in one or the other direction along the hard axis, this producing magnetization in the domain of the films as shown at a (a " 1 " state) or e (a " 0 " state) in Fig. 2. The effect of a hard direction field in the same direction as the remanent magnetization stored in the film (a " pulling " field) is shown at b, that of a smaller over-lapping easy direction field is at c and that of an opposing hard direction field (" pushing " field) is at d. The thin film may be arranged to have adjacent strip-like regions 14, 15, 16, 17 (Fig. 6, not shown) running in the average easy direction, the easy directions 17 in the individual strips being angled alternately on either side of this average direction, (i.e. " rippled "). This can be effected by annealing the film using a combination of a strip matrix of adjacent strips of permanent magnet material (cobalt) magnetized alternately in opposite hard directions and an uniform easy direction field. Alternatively the hard magnetic strips may be deposited on a soluble coating on the thin film (Fig. 17, not shown) and permanently magnetized using a strip matrix before annealing the film, the coating being dissolved subsequently. Read-out is by opposing very short pulses +i xL , - i xL  (Fig. 4) in conductor 4 (Fig. 3, not shown) with a long overlapping pulse in conductor 5. If a " 0 " is stored an output 10 is obtained in conductor 6 (Fig. 3, not shown), the magnetic vectors in the film dot being rotated from the position shown at e (Fig. 2) to the position at c. If a " 1 " is stored, outputs 11, 12 and 13 are obtained and signals 12 or 13 can be used for identification. Additional pulses +i xs , -i xs  are used for rewrite, the long +i y pulse being extended as shown in dash lines if a 0 is to be rewritten (to prevent - i xs  from writing a " 1 "), the signal read controlling the rewrite. In an alternative method a very short positive hard direction pulse is applied coincidently with a longer easy direction pulse (Fig. 5, not shown). If a " 1 " is stored an output is again obtained as at 11 (Fig. 4) and a following short pulse then rotates the vectors to the hard direction and thus rewrites the " 1." If a " 0 " is stored the positive hard direction pulse is too short to switch the magnetic vectors from the " 0 " (hard) direction to the " 1 " (hard) direction and merely produces the " pushing " effect shown at d in Fig. 2, so that the longer easy direction pulse has no effect and the film reverts to its " 0 " condition (e in Fig. 2). So that the film dot is subjected to an equal number of opposite pulses two negative hard direction pulses can then be applied. This is unnecessary if the easy directions in alternate parallel strip-like zones of the film are " rippled " as described above. When the " pushing " field can be up to 70% greater than the pulling field and the duration of the " pushing " field pulses need not be limited. Three state storage films.-Recording " 1," " 0 " or " empty " can be formed by providing in the films strip-like regions oriented in the easy direction and differing alternately in the energy barrier which must be overcome to rotate the magnetic vector in the region from one easy direction to the other. In Fig. 8 the regions 106 having a high energy barrier have magnetic vectors with a double arrow. A field having an easy direction component to the left and limited so that the end of its vector falls into the area 107 in Fig. 9 will write in a " 1 " as shown at c in Fig. 8 if the film is in the " empty '' state a. If no " 1 " is stored and no output occurs a second pulse is sent to test for a " 0 " state (the opposite state to c in Fig. 8). For read-out the film can be set to the " empty " state as at a, Fig. 8, by a field limited to give a vector entering region 109 or 110 in Fig. 9. The higher energy barrier regions may be obtained by increased thickness of those regions or using for them a suitably different magnetic material or by having the magnetic material of those regions (or a copper base under them) vapour deposited obliquely on to the substrate. Alternatively their impurity atom concentration can be increased by deposition. To read out from a matrix of such films reading pulses hx hx -, -, hy (or hx, hy) and a steady field - HxP 2 2 (Fig. 15, not shown) may be used, the first three being sent through different conductors 126<SP>11</SP> 127<SP>1</SP> and 128<SP>111</SP> (Fig. 16, not shown) of three sets of conductors. The film read out is then in the empty state and 0 or 1 is written in by suitable hard direction pulse in a fourth conductor traversing all the elements of the matrix.