Everything about Permalloy totally explained
Permalloy is the 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. 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 electrical
resistivity generally varies within the range of 5% depending on the strength and the direction of an applied
magnetic field. Permalloys typically have the
face 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 sensors. In its initial application, Permalloy was wrapped around the insulated copper conductors of telecommunication cables, reducing signal distortion through improved inductive compensation of cable
capacitive reactance.
The right conditions for transmitting signals through cables without distortion were first worked out mathematically by
Oliver Heaviside. After a prolonged search, 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.
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 at
Bell Labs in 1940. At the time, when used in long distance copper telephone lines, it allowed a tenfold increase in maximum line working speed.
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