MAGNETIC ALLOYS 131 



applications where distortion and energy loss are fatal to good quality 

 of transmission. The resistivity of this alloy is only 18 microhms- 

 centimeter, but it can be increased without serious sacrifice of the low 

 hysteresis characteristic by adding molybdenum. The alloy chosen 

 for commercial use is 7-45-25 Mo-perminvar, having a resistivity of 

 80 microhms-centimeter. 



The manner in which molybdenum affects the magnetic properties is 

 illustrated in Figs. 3, 4, and 6. The permeability is not quite so inde- 

 pendent of the magnetizing force as for the alloy without molybdenum, 

 nor is the hysteresis loss quite so low. The initial permeability for 

 the alloy baked the customary 24 hours is somewhat higher. When 

 baked for a longer period the magnetic characteristics tend more 

 toward those of 45-25 perminvar. 



Permendur 



• 



An alloy in the iron-cobalt series used in communication apparatus is 

 permendur. The typical composition is 50 per cent iron, 50 per cent 

 cobalt. The outstanding magnetic property of this alloy is high 

 permeability in the range of flux densities between 12,000 and 23,000 

 gausses (Figs. 4 and 6). The high permeability of this alloy "endures" 

 to higher flux densities than does the permeability of any other mag- 

 netic material. Its initial permeability is about 700, though values as 

 high as 1,300 have been observed for some samples. In addition to the 

 high permeability at high flux densities permendur also has a relatively 

 flat "butterfly" curve, as may be seen in Fig. 7. For a superposed 

 d.-c. magnetizing force of 10 oersteds the a.-c. permeability of " Armco " 

 iron is 40, as compared with 200 for permendur. 



1.7 V -Permendur 



Permendur is difficult to roll into sheets, because of its brittleness. 

 To overcome this difficulty 1.7 per cent vanadium is added. With 

 this addition it may be rolled into sheets as thin as a few thousandths 

 of an inch. Th s amount of vanadium affects the magnetic properties 

 only slightly, although larger amounts decrease the permeability at 

 high flux densities. 



Another improvement incident to the addition of vanadium is a 

 fourfold increase of resistivity from its value of 6 microhms-centimeter 

 for simple permendur. Permendur, it may be noted, has the lowest 

 resistivity of the iron-cobalt series. 



Laboratory Results 

 As stated hereinbefore, all the alloys that have been discussed have 

 been made on a factory scale for some use in the telephone plant. 



