magnetic alloy
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Magnetic alloys
Nickel is a versatile element and will alloy with most metals. Complete solid solubility exists between nickel and copper. Wide solubility ranges between iron, chromium, and nickel make possible many alloy combinations.
Magnetic alloys are alloys engineered to have special magnetic properties.
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.
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.
Supermalloy is an alloy composed of Ni (79%), Mo (5%), and Fe.
It is a magnetically soft material. The resistivity of the alloy is 6 nΩ·cm2/cm. It has a high magnetic permeability and a low coercivity. Supermalloy is used in manufacturing of components of radio engineering, telephony, and telemechanics instruments.
