8 BELL SYSTEM TECHNICAL JOURNAL 



are about 10~* of the electrostatic forces. The difference is even 

 greater when electrostatic forces between electrons and nuclei, or 

 between nuclei, are compared with magnetic forces. The magnitudes 

 of these forces for a specific hypothetical arrangement are shown in 

 Fig. 5. 



/" 



)N(^< 



ELECTRON { ^<- 



/ 

 / 



/ ELECTROSTATIC FORCES 



j IN DYNES 



H 2 X 10-3 



-*o 



NUCLEUS 

 + 26 6 



c 



MAGNETIC FORCES IN DYNES 

 — ORBITAL MOTIONS, 2X10"^ — 

 SPINS, 3 X lO-l'* 



ELECTRON 



-e 



Fig. 5 — The magnitudes of the forces in a hypothetical iron-like atom, showing that 

 electrostatic forces are more powerful than magnetic forces. 



Consider the magnitude of magnetic forces from another point of 

 view. The magnetic energy of a permanent magnet of moment ha 

 in a field of strength H is 



E = - ^iAH, 



when fXA and H are parallel. In a magnetic substance we may regard 

 the atomic magnets as being held parallel by a fictitious field Hi. 

 When the material is heated to the Curie temperature, 6, the energy 

 of thermal agitation (~ kd) destroys the alignment of the atomic 

 magnets by the fictitious or "internal" field Hi. Then 



kd ^ ixAHi. 



For iron, 6 = 1043° K. and ma = 2.04 X 10-2« erg/gauss, thus the 



