64 



BELL SYSTEM TECHNICAL JOURNAL 



TABLE I 



Some Extremes in the Properties of Magnetic Materials Available in 1915, 



AND IN 1935 



Material 



Iron 



Iron-nickel ". . . . 



Silicon-iron 



Iron 



Iron-cobalt -nickel 

 "permin\"ar". . 



Iron-cobalt 



Tungsten steel . . . 

 New K. S. steel . . 



Property 



Maximum permeability. . 



Initial permeability 



Coercive force in oersteds. 



Maximum permeability . . 



Initial permeability 



Coercive force in oersteds . 



Initial permeability. 



Hysteresis at Bj^ = 100 gausses, in ergs 

 per cm.3 per cycle 



Hysteresis at 5m = 100 gausses, in ergs 

 per cm.' per cycle 



Saturation value in gausses •' 



Permeability at 5 = 16,000 gausses. 



Coercive force ^ in oersteds . 

 Coercive force -^ in oersteds. 



Value 

 1915 



45,000" 

 300 

 0.311 



2,800' 

 700' 

 1.51" 



400 



20 



25,800 

 2,100 



80 



Value 

 1935 



340,00012 



20,00012 



0.03' 2 



600,000'5 



12,0001^ 



O.Ol's 



2,000'2 



0.1'= 



0.00003'* 



25,800 

 19,000i8' 12 



80 

 900 



Superior numerals refer to references at end of paper. 



compositions (alloys), and new methods of heat treatment. Some of 

 these figures refer only to laboratory specimens, and not to materials 

 available in commercial quantities. 



But the chief topic of this paper is the theoretical side of ferro- 

 magnetism. How is one to explain the different values of magnetic 

 permeability, ranging from 1 to 600,000 for various materials? Or, 

 to consider first the more fundamental questions, what is the ele- 

 mentary magnetic particle, and why is ferromagnetism associated 

 with so few elements? 



Origin of Ferromagnetism 



It was suggested by Ampere about one hundred years ago that 

 molecules might behave as magnets because of the electric currents 

 circulating in them. Today, with the advance in knowledge of atomic 

 structure, the origin of ferromagnetism can be discussed in more 

 specific terms. Strangely enough, the spectroscopists have supplied, 

 so to speak, the elementary magnetic particle. It is the spinning 

 electron. In order to explain their extensive observations on spectral 

 lines, they found it necessary to revise the picture of the atom. For 

 some time it has been supposed that an atom was made of a heavy 

 nucleus with a positive charge and of electrons moving in circular 



