New approach to high-speed storage - Low flux density materials

Abstract

This paper presents a new approach toward overcoming the factors currently limiting the frequencies at which storage devices may be switched from one information state to another. Ferrite elements for random access storage have been developed which require a fraction of a microsecond for a cycle. Thus the ferrite switching time establishes a maximum switching rate given by the inverse of the total switching time in a cycle. However, operation of elements such as these in a large capacity memory at rates limited only by switching times is usually prevented by: deterioration of magnetic properties due to heating effects, increase in selection line impedance, and long transmission delays. A series of ferrimagnetic oxides have been developed with properties such that the limits on minimum cycle time are appreciably extended. The most important of these properties is the saturation flux density. Over a range of composition, flux densities have been obtained which extend from 100-500 gauss. The lower flux density results in an appreciably lower energy dissipation in the magnetic structure and consequently in higher switching rates for a given temperature rise within the magnetic material. In addition, temperature dependence of those magnetic properties which determine storage applicability is more favorable than with the better known ferrites. Toroids have been fabricated with these materials which are suitable for random access memories. These elements have been operated successfully in free air at repetition frequencies in excess of 2 Mc. The improvements in array characteristics that result are discussed in terms of impedances and transmission delays. © 1960 The American Institute of Physics.