Linear ferrites for read-only store application

The development of a linear ferrite core used in an inductively coupled read-only store application is described. In addition to the normally desired linear relation between B and H , the application also requires wide-range temperature stability and low magnetostrictive ringing. A Ni-Zn ferrite, which was proposed for the application, was determined to be inadequate in its performance. However, it was found that if the cores were vibrated at an ultrasonic frequency in a slurry of fine abrasive and alcohol, the pulse properties of the devices were improved. While the reversible permeability was decreased by the processing, the linearity of the B-H curve was improved and the hysteresis losses were decreased. Also, the magnetostrictive ringing decreased and temperature stability improved. Further tests, which were made in an attempt to understand the phenomenon, showed that the improvement in properties resulted from a stress-induced anisotropy caused by the vibration in the slurry.