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The purpose of the core is to provide a closed high permeability path for the magnetic field lines. B – magnetic field in the core will be approximately constant across any cross section B F – "fringing fields". In the gaps G the magnetic field lines "bulge" out, so the field strength is less than in the core: B F < B
Cobalt-iron alloys like permendur have very high Curie temperatures so they can function magnetically at high temperatures at which other ferromagnetic materials lose their magnetic properties. They are harder and less ductile than many other iron alloys and so are harder to fabricate, but have superior mechanical strength.
For example, 4% electrical steel has an initial relative permeability (at or near 0 T) of 2,000 and a maximum of 38,000 at T = 1 [5] [6] and different range of values at different percent of Si and manufacturing process, and, indeed, the relative permeability of any material at a sufficiently high field strength trends toward 1 (at magnetic ...
In 2009, a team of MIT physicists demonstrated that a lithium gas cooled to less than one kelvin can exhibit ferromagnetism. [12] The team cooled fermionic lithium-6 to less than 150 nK (150 billionths of one kelvin) using infrared laser cooling. This demonstration is the first time that ferromagnetism has been demonstrated in a gas.
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
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.
In the gaps G the electric field lines "bulge" out, so the field strength is less than in the core: B F < B B L – leakage flux; magnetic field lines which don't follow complete magnetic circuit L – average length of the magnetic circuit. It is the sum of the length L core in the iron core pieces and the length L gap in the air gaps G.
Hysteresis loop Induction B as function of field strength H for H varying between H min and H max; for ferromagnetic material the B has different values for H going up and down, therefore a plot of the function forms a loop instead of a curve joining two points; for perminvar type materials, the loop is a "rectangle" (Domain Structure of Perminvar Having a Rectangular Hysteresis Loop, Williams ...