Patent GB-997777-A (GB)
Title: Improvements in and relating to magnetostrictive devices
IPC: G11B5/62
Filed: 1963-08-26
Abstract: 997,777. Magnetic pulse-storage apparatus; electromechanical delay lines. INTERNATIONAL BUSINESS MACHINES CORPORATION. Aug. 26, 1963 [Nov. 30, 1962; Aug. 27, 1962 (2)], No. 33643/63. Headings H3B and H3U. A storage device comprises an elongated thin film 18 of magnetostrictive material deposited on a substrate 10 through which a stress wave is propagated such that a magnetic state established in a first region of the film by a magnetic field is propagated to a second region of the film. As shown in Figs. 1 and 2, a nickel-iron magnetostrictive film 18 on a quartz substrate 10 is subjected to a mechanical tension and compression wave 28 from generator 14 and transducer 12 and to a magnetic field produced by signal input generator 24 coupled to input conductor 20. The series of tension and compression waves cause the film 18 to exhibit an induced longitudinal anisotropy in the zones A, C, E and an induced transverse anisotropy in the zones B, D, F along the easy Y axis. Binary information may be entered into the circuit of Fig. 1 when the portion of film 18 coupled by input conductor 20 is subjected to mechanical induced longitudinal anisotropy due to tension, by applying a current pulse to the conductor 20 so as to produce a magnetic field to the right or left along the longitudinal axis. The magnetization of the zone A then takes up the position as shown in Figs. 3a, 3c, 3e dependent upon the direction of the magnetic field produced by conductor 20. The NÚel wall thus initiated is propagated along the film 18 by the stress wave as shown in Fig. 3. The change in magnetization of the last zone F is detected by output conductor 22 connected to load 26. In order to ensure that the magnetization of each of the zones of film 18 orients itself in the same direction along the easy axis during the period when the zone is exhibiting an induced transverse anisotropy, the film is subjected to a magnetic bias along its easy axis by a pair of Helmholtz coils. In order to store the information the output conductor is coupled back to the input. In the arrangement of Fig. 4 (not shown) the absorbing plate 16 of Fig. 1 is replaced by a second source and transducer supplying a stress of the same frequency and amplitude as that delivered from source 14. By varying the phase of this second source to be 180 degrees out of phase the two stress waves cancel out, so that a domain wall being transferred towards the output conductor remains in the zone it is in on application of the second wave. The direction of travel of the domain walls along the longitudinal axis may be reversed by appropriate choice of the phases of the two waves. In the embodiments of Fig. 6 (not shown) and Fig. 9 the input and output conductors 21<SP>1</SP>, 23<SP>1</SP> are positioned as shown transverse to the easy axis Y of the magnetostrictive film 118<SP>1</SP>. The input conductor 21<SP>1</SP> is energized by input means 124<SP>1</SP> to apply a magnetic field along the easy axis, Fig. 8 (not shown), such that a magnetic domain wall is established which is propagated along the film by the stress wave from source 114<SP>1</SP>. Information is thus represented by the presence or absence of a domain wall, which domain wall is sensed by output conductor 23<SP>1</SP>. Control coil 130 is energized by selectively operable current source 132 to apply a magnetic field directed transverse with respect to the plane of the film 118<SP>1</SP>. The thickness of the film is made such that NÚel walls are established, i.e. the magnetization vectors rotate from one direction to another within the plane of the film, and these walls are propagated along the film. However, when control coil 130 is energized the magnetization vectors of the film are rotated out of the plane of the film in each place where a NÚel wall exists so that a Bloch wall is established, i.e. wherein the magnetization vectors rotate from one direction to another by spirally rotating out of the plane of the film, Fig. 10 (not shown). Thus coincidence of both stress-induced anisotrophy and domain vector orientation within the plane of the film is absent and the domain wall is not propagated, thereby allowing the information to be permanently stored in the film.