Magneticfilms are used in the information processing area in two principal applications: random access high speed memory and serial 8ccee.s lower speed memory. The application requirements for magnetic films of these t w o types, the material properties needed to meet these requirements, and the metellurgical structures which give rise to the properties are described. The directions of present development work and of possible future improvements in the technology are discussed.T IS THE PURPOSE of this paper to provide a simplified view of the present status of our understanding of the film material requirements for the two principal computer applications of films-namely, main memory and disk and tape memory. To do this, we will first establish the interrelations between the application oriented parameters and the material parameters. The appropriate material parameters and their physical origin will then be discussed.
I. HIGH S p m MEMORY FILM MATEW A . BackgroundThin magnetic films were h t proposed as high speed main memory elements by Blois [l] in 1955. The early predictions that batch fabricated thin film memories would soon completely replace core memories encountered two difEculties. First, many unanticipated effects made achieving the required reproducibility and uniformity over large areas (hundreds to thousands of bits) a laborious and time consuming task. Second, less than half the cost of a typical core memory is in the array, and the nonlinearity of the core may be used to assist in reduction of memory electronics cost; films must achieve nondestructive readout (NDRO) in order to have comparable or lower cost electronics, and this aggravates the reproducibility and uniformity problem. The k t commercial appliction of a 6lm memory attempted to avoid these' problems by exploiting their natural performance advantage (inherent higher speed) in a small scratch pad; but the much heralded semiconductor memories rapidly eroded this opportunity. Even with these difficulties, which required over a decade to surmount, f i l m memories have been and are being designed into commercial computer systems (Fig. 1). They are emerging as the dominant tedmology in areas where nonvolatility, low power, NDRO, radiation resistance, or some combination of these is important in system design.
B. Material and Array Characteristics versus Memory OperationThe dominant film material used for high speed random access memories is the zero magnetostrictive alloy of 81.5-percent Ni-18.5-percent Fe. Its use in a memory depends on the two stable magnetic states of high remanence B, in zero applied field, as indicated in Fig. 2. The stability of the magnetization in each state is of prime concern since the integrity of the stored information depends on this, and much work has gone into understanding how to obtain films, and design film arrays, which resist demagnetization from various stray field effects. Shielding provides protection from external fields but fields may arise internally from adjacent "bits" of information, from induced ...
