Two-Phase Permalloy for High-Speed Switching

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Abstract
The addition of gold to Permalloy has made it possible to precipitate a second phase in the alloy. As a result it is possible to control the coercive force and, to some degree, the threshold for rotational flux reversal, by appropriate heat treatments. On this basis a series of alloys have been developed by adding 2–14% gold to Permalloy. Some of these alloys have switching times approximately four times faster than that of the standard Permalloy composition. The switching time is defined as the reversal time at twice the coercive force. The alloy is prepared by annealing at the solution temperature of 900°C and then cooling rapidly. This is followed by cold rolling tape from approximately 0.014– to 0.00013-in. thickness, which is the thickness for switching applications. The material is then annealed at 600–650°C. Under these conditions, alloys containing 7% gold and 14% gold yield square hysteresis loops having coercive forces of at least 1.7 and 4.3 oe, respectively. For the 7% gold alloy, the threshold for rotational flux reversal is 2.5 oe.

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