. The Bell System technical journal . o as to make a hollow parallelogram with sides parallel to the(100) crystal axes, and annealed in H2 below the 01-7 transformationpoint. The highest permanent magnet quality has been attained witha platinum cobalt alloy ^^ costing some $400 per pound. One of the main objectives of commercial magnetics research hasbeen the attainment of higher permeabilities—initial, maximum,reversible, and at high flux densities. The reversible permeability isclosely linked with the initial permeability and saturation flux permeability at high flux densities *^
. The Bell System technical journal . o as to make a hollow parallelogram with sides parallel to the(100) crystal axes, and annealed in H2 below the 01-7 transformationpoint. The highest permanent magnet quality has been attained witha platinum cobalt alloy ^^ costing some $400 per pound. One of the main objectives of commercial magnetics research hasbeen the attainment of higher permeabilities—initial, maximum,reversible, and at high flux densities. The reversible permeability isclosely linked with the initial permeability and saturation flux permeability at high flux densities *^ appears to be susceptible toconsiderable increases by proper treatment of materials. The initialpermeability can be increased by proper technique, but such gainsare frequently sacrificed in practice because of unavoidable mechanical « P. P. Cioffi & O. L. Boothbv, Phys. Rev. 55, 673 (1939).« W. Jellinghaus, Zeit. Tech. Phys. 17, ii (1936).«For example, at 5 = 10,000, or 5 = 20,000. MAGNETIC MATERIALS IN TELEPHONE SYSTEM 463. 1920 1939 COMMERCIAL EXPERIMENTAL =_ZERO THEORETICALLIMIT Fig. 11—Improvements in the properties of magnetic materials since 1920,in relation to theoretically possible properties. 464 BELL SYSTEM TECHNICAL JOURNAL stresses, or because of large eddy current shielding. Higher maximumpermeabilities than now attainable do not promise great , the low values of coercive force and hysteresis loss foundwith materials having high maximum permeability may be sufficientlydesirable, regardless of permeability needs. Another important objective of magnetics research has been toreduce energy losses. Hysteresis loss at low flux densities, as indicatedby the loop area coefficient a, should be decreased to cut down har-monic generation and modulation in magnetic core coils. Perminvarhas shown desirably reduced losses, but it is sensitive to magnetic andmechanical conditions. Eddy currents are controlled by resistivityand degree of subdivision of the m
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