Time and amplitude resolution of a thin film matrix recording device

The structure of the film element used in the magnetic matrix recorder is described. The amplitude resolution is proportional to the digit margin, the ratio of digit current required to disturb to that required to write. An experimental curve of this parameter versus film thickness is given. Experimental curves of time response of the recording element are presented. The differential equation for the behavior of the magnetization in a thin film recording element is solved for several cases of interest; the time resolution (the smallest time between a small signal of one polarity and a large signal of the other such that the recorder does not make a mistake on the small signal) is given as a function of the anisotropy of the film and the applied hard axis field before and during the measurement. The resolution time is inversely proportional to the square root of the sum of the anisotropy field and the applied hard axis restoring field; time resolutions range from 1.4 ns for a permalloy film with an Hkof 3 Oe to 0.15 ns for a cobalt film with an Hkof 48 Oe or a permalloy film in which a large hard axis restoring pulse is used. This corresponds to an errorless frequency response of 350 MHz and 3330 MHz, respectively.