New Magnetic Materials

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Abstract
With the rapid growth of the radio and communication industry, a need for magnetic materials having special properties for this particular application has developed. A number of nickel-iron alloys, such as permalloy, nicaloi, Mu Metal, and variations of these have found wide application as they all have the common property of high permeability at relatively low inductions. Where high resistivity also is desired, additional alloying elements, such as chromium and molybdenum, have been added. Complete freedom from strain, either mechanical or chemical, is necessary for good magnetic quality, and the strain set up by magnetization can be compensated for in many cases by heat treatment in a magnetic field. Silicon-iron alloys and some of the nickel-iron alloys can be very much improved by a combination of cold-rolling and heat treatment which induces a high degree of preferred orientation. This cold-rolled strip has found wide application in various types of electrical apparatus. Permanent-magnet alloys of the alnico type have been very greatly improved recently so that the external energy factor (BHmax) is now about three times what it was in the best alnico heretofore available. Comparative data on the different types of permanent-magnet steels and alloys are given, and the new material should find wide application in the radio field. Considerable saving in material and size and weight of apparatus can be made by the application of these outstanding recent developments in magnetic materials provided suitable changes in design are made to allow for the most economical use.

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