- Permalloy
Permalloy is the term for a
nickel iron magneticalloy . Generically, it refers to an alloy with about 20% iron and 80% nickel content. Permalloy has a high magnetic permeability, lowcoercivity , near zeromagnetostriction , and significantanisotropic magnetoresistance . The low magnetostriction is critical for industrial applications, where variable stresses in thin films would otherwise cause a ruinously large variation in magnetic properties. Permalloy's electricalresistivity generally varies within the range of 5% depending on the strength and the direction of an appliedmagnetic field . Permalloys typically have theface centered cubic cystal structure with a lattice constant of approximately 0.355 nm in the vicinity of a nickel concentration of 80%.Permalloy is used in transformer laminations and magnetic
recording head sensor s. In its initial application, Permalloy was wrapped around the insulated copper conductors of telecommunication cables, reducing signal distortion through improved inductive compensation of cablecapacitive reactance .The right conditions for transmitting signals through cables without distortion were first worked out mathematically by
Oliver Heaviside . [Bragg, L. "Electricity" (London: G. Bell & Sons, 1943) p. 212-3.] After a prolonged search, Permalloy was discovered in 1914 byGustav Elmen ofBell Laboratories , who found it had higher permeability thansilicon steel . Later, in 1923, he found its permeability could be greatly enhanced by heat treatment.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 . The latter was invented atBell Labs in 1940. At the time, when used in long distance copper telephone lines, it allowed a tenfold increase in maximum line working speed. [Bragg, L. "Electricity" (London: G. Bell & Sons, 1943) p. 212-3.]ee also
*
Mu-metal .
*Sendust .
*Supermalloy a material with even higher magnetic permeabilityReferences
* 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.
Wikimedia Foundation. 2010.