Thin tapes of high-purity silicon — Iron for magnetic amplifiers

Abstract

THE CHOICE of magnetic material for use in magnetic amplifiers is related to the requirements placed upon the amplifier. In the case of low- and medium-performance amplifiers, any good ferromagnetic material may be suitable; for high-performance amplifiers, however, the ferromagnetic core material must more closely approximate that which is considered the ideal magnetic material for magnetic amplifiers. Such an ideal material would be characterized by high saturation flux density, zero differential permeability in the saturation branch of the dynamic hysteresis loop, infinite permeability below the knee of the loop, and losses and coercive force that approach zero. 1,2 Thus, silicon-iron, which has a high saturation flux density compared to other magnetic materials such as Deltamax (an oriented 50% Ni−50% Fe alloy), finds little use in high-performance magnetic amplifiers because of its relatively high coercive force and lack of loop squareness, particularly in laminations less than about 0.004 inch thick. Deltamax, which has a lower saturation flux density than silicon-iron, is used to a considerable extent in magnetic amplifiers because it has lower coercive forces and higher values of squareness than silicon-iron. The advantage of the higher saturation flux density of most silicon-irons is lost when the material is used in a magnetic amplifier. Yet, because of its high saturation flux density, silicon-iron would be useful in magnetic amplifiers if the a-c coercive force were lower and the induction at low magnetizing forces were higher. Such improvements in magnetic properties of silicon-iron have been obtained by utilizing and controlling differences in surface energy to act as the driving force for crystal growth. 3–5 Sharply improved (110) [001] crystal orientations, compared to commercial-oriented silicon-iron, have been obtained in sheets and tapes of high-purity silicon-iron from 0.001 to 0.012 inch thick. 3