Nickel-iron metal-tape materials for information storage

Of the alloys having a rectangular hysteresis loop, certain nickel-iron-molybdenum alloys are the most attractive for information-storage applications. The properties required of the material differ with the type of storage device. Two groups of alloys have been prepared by powder metallurgy; one containing about 4% molybdenum and the other about 12% molybdenum. These materials must be rolled to about 0.5 mil to achieve a reasonably rectangular hysteresis loop and fast switching; the best compromise between these two conflicting requirements is obtained with final reductions of about 50%. The coercivity can be made to have any value between 0.05 and 2 Oe by suitable final heat treatment. When measured with a maximum field of 1 Oe the squareness of the best 4% molybdenum alloy is 0.88 and the switching time is 0.7 ¿s; the 12% molybdenum is a little less square and has half the switching time. In any device in which a switching field of about 1 Oe is suitable (e.g. the shift register) both these materials are faster than ferrites. When a discriminatory action is required, alloy tapes can be used with very small fields but they switch more slowly.