462 BELL SYSTEM TECHNICAL JOURNAL 



the regular 2-81 Mo-permalloy powder of a small amount of permalloy 

 powder containing about 12.5 per cent of molybdenum. The latter 

 material has a Curie point just above room temperature. 



Conclusion: Desirable and Possible Improvements 



It appears from the above inspection of the magnetic elements of 

 apparatus that there is a general desire for all properties which con- 

 tribute to magnetic effects to be increased, and for those which cause 

 apparatus energy losses to be decreased. A considerable success has 

 already been achieved in these directions. The obstacles to further 

 improvement are in part difficulties in commercial application of 

 laboratory techniques, and in part ultimate limitations to the properties 

 of materials. 



The chart in Fig. 11 shows the recent trend toward the realization 

 of the best possible magnetic properties in new materials or by im- 

 proved processes. Values are given for the year 1920 (i.e. before com- 

 mercial application of the permalloys), for 1939 as commercially and 

 as experimentally realized, and for what may be considered as the 

 attainable limit. It is evident that most of the properties which could 

 be improved have been improved in commercial materials by a factor 

 of ten or so within the last twenty years. A further improvement of 

 several properties by a factor as large as ten has been observed by 

 experimental procedures. These improvements have not been utilized 

 in all cases, either because they may not be of great practical value, 

 or because they involve processes which are commercially impracti- 

 cable, or materials which are very expensive. Thus, the highest 

 value of n,n has been attained on a single crystal of H2 purified iron ^* 

 cut so as to make a hollow parallelogram with sides parallel to the 

 (100) crystal axes, and annealed in H2 below the 01-7 transformation 

 point. The highest permanent magnet quality has been attained with 

 a platinum cobalt alloy "^^ costing some $400 per pound. 



One of the main objectives of commercial magnetics research has 

 been the attainment of higher permeabilities — initial, maximum, 

 reversible, and at high flux densities. The reversible permeability is 

 closely linked with the initial permeability and saturation flux density. 

 The permeability at high flux densities *^ appears to be susceptible to 

 considerable increases by proper treatment of materials. The initial 

 permeability can be increased by proper technique, but such gains 

 are 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. 



