The crosstie memory

The crosstie memory stores information in magnetic domain walls in permalloy films about 350 Å thick. The domain walls are also used as shift register tracks. Serrated edges on narrow thin film permalloy strips are used to center a domain wall in each strip and to provide stable positions for crossties and Bloch lines. A magnetoresistance detector uses the same information bearing permalloy film as the magnetoresistive element. The entire crosstie memory can be fabricated on a silicon wafer or chip using conventional photolithographic procedures as are used in fabricating integrated circuits. Thus, a magnetic memory can be combined with semiconductor drivers, decoders, and sense amplifiers on the same chip. The memory is intended to serve as a block oriented random access memory (BORAM). Important background information such as static and dynamic stability conditions, Bloch line mobility, propagation and observation techniques are reviewed. Also, design goals and the role such device is expected to play in memory technology are presented. Anticipated performance includes a shift rate of 20 × 10⁶bits/sec, a bit density greater than 1.5 × 10⁵bits/cm², an operating temperature range from -50 °C to 100 °C, nonvolatility, low cost, and low power consumption.     

Magnetic thin-film magnetometers for magnetic-field measurement

Thin magnetic-film magnetometers used for magnetic-field measurement are reviewed and compared. A large variety of magnetic thin-film magnetometers have been constructed, and in some cases their properties are unique. A summary of thin-film magnetometers and their performance is provided.     

A sensitive magnetoresistive power amplifier

A small, sensitive, low noise, high gain power amplifier, using the anisotropic magnetoresistance effect in thin film permalloy, has been designed and its characteristics calculated. The minimum detectable input current is determined by Johnson noise and hence by input resistance and desired bandwidth. An example of theoretical performance is as follows. For an amplifier unit with approximate dimensions of300 times 300 times 2 mum and with input and load resistances of 50 Ω each the calculated noise at room temperature is equivalent to 10^-8A for a bandwidth (BW) of 1MHz or to 10^-7A for a BW of 100 MHz. At the 10^-8A input current level, the calculated power gain issim 600,000corresponding to a current gain of 775. Power gain decreases with input current asI^{-4/3}, reaching unity atI = 2.1 times 10^{-4}A. Hence, for a BW of 1 MHz, at room temperature, the input current operating range for both amplification and signal-to-noise ratio greater than one is fromI=10^{-8}A to2.1 times 10^{-4}A. To achieve high gain, the amplifier is configured so that the magnetization of the permalloy is biased to lie nominally along the hard axis, the sensing current in the permalloy makes an angle of 45° with the nominal magnetization direction, and the input current produces a magnetic field along the easy axis. This microsize, low noise, silicon compatible power amplifier will be useful in digital and FM applications and possibly as an amplifier for crosstie and bubble memories.