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Paramagnetism, ferromagnetism, and spin waves. Ferromagnetism is a property of certain materials (such as iron) that results in a significant, observable magnetic permeability, and in many cases, a significant magnetic coercivity, allowing the material to form a permanent magnet.
Strip of permalloy. Permalloy is a nickel–iron magnetic alloy, with about 80% nickel and 20% iron content.Invented in 1914 by physicist Gustav Elmen at Bell Telephone Laboratories, [1] it is notable for its very high magnetic permeability, which makes it useful as a magnetic core material in electrical and electronic equipment, and also in magnetic shielding to block magnetic fields.
Permendur rods. Permendur is a cobalt-iron soft ferromagnetic alloy with equal parts of cobalt and iron which is notable for its high magnetic saturation level. [1] [2] Its saturation flux density of around 2.4 tesla is the highest of any commercially available metal.
Magnetite is black or brownish-black with a metallic luster, has a Mohs hardness of 5–6 and leaves a black streak. [7] Small grains of magnetite are very common in igneous and metamorphic rocks. [11] The chemical IUPAC name is iron(II,III) oxide and the common chemical name is ferrous-ferric oxide. [12]
Mu-metal has several compositions. One such composition is approximately 77% nickel, 16% iron, 5% copper, and 2% chromium or molybdenum. [1] [2]More recently, mu-metal is considered to be ASTM A753 Alloy 4 and is composed of approximately
The concept of permeability is of importance in determining the flow characteristics of hydrocarbons in oil and gas reservoirs, [4] and of groundwater in aquifers. [5]For a rock to be considered as an exploitable hydrocarbon reservoir without stimulation, its permeability must be greater than approximately 100 md (depending on the nature of the hydrocarbon – gas reservoirs with lower ...
Permeation can occur through most materials including metals, ceramics and polymers. However, the permeability of metals is much lower than that of ceramics and polymers due to their crystal structure and porosity. Permeation is something that must be considered carefully in many polymer applications, due to their high permeability.
Soft ferrites are not suitable to make permanent magnets. They have high magnetic permeability so they conduct magnetic fields and are attracted to magnets, but when the external magnetic field is removed, the remanent magnetization does not tend to persist. This is due to their low coercivity.