Permalloy

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Permalloy is term for a nickel iron magnetic alloy. Generically, it refers to an alloy with about 20% iron and 80% nickel content. Permalloy has a high magnetic permeability, low coercivity, near zero magnetostriction, and significant anisotropic magnetoresistance. This alloy is used in transformer laminations and magnetic recording head sensors. Permalloy's electrical resistivity generally varies within the range of 5% depending on the strength of the magnetic field. The low magnetostriction is critical for industrial applications, where variable stresses in thin films would otherwise cause a ruinously large variation in magnetic properties.

Other compositions of Permalloy are available, designated by a numerical prefix denoting the percentage of nickel in the alloy, for example 45 Permalloy containing 45% nickel, and 55% iron. Molybdenum permalloy is an alloy of 81% nickel, 17% iron and 2% molybdenum. Invented at Bell Labs in 1940, it provides improved inductive compensation of capacitive reactance in long distance telephone lines.

Permalloy was discovered in 1914 by Gustav Elmen of Bell Laboratories, who found it had higher permeability than silicon steel; later, in 1923, he found its permeability could be greatly enhanced by heat treatment.

[edit] See also

Mu-metal.

[edit] References

Richard M. Bozorth, Ferromagnetism, Wiley-IEEE Press (1993 reissue), ISBN 0-7803-1032-2.
P. Ciureanu and S. Middelhoek, eds., Thin Film Resistive Sensors, Institute of Physics Publishing (1992), ISBN 0-7503-0173-2.