74 



BELL SYSTEM TECHNICAL JOURNAL 



CRrSTAL 

 AXES 



SATURATED 



Fig. 8 — Domains in a single crystal of iron. 



increasing the resultant magnetization in the direction of the field. 

 These changes take place suddenly, and they are the cause of the 

 Barkhausen effect; each sudden change in orientation of a domain 

 accounts for one step in the magnified magnetization curve shown in 

 Fig. 5, or for one click heard in the telephone receiver when listening to 

 the Barkhausen effect. 



There is even more direct evidence of the existence of domains in a 

 piece of iron. The iron is placed under a microscope with a magnifica- 

 tion of 500, and is covered with a colloidal suspension of iron oxide.^' 

 It is found (Fig. 9) that the colloidal particles are concentrated along 



(a) 



(b) 



(c) 



Fig. 9 — Powder-patterns for iron (McKeehan and Ellmore): (left) field outward; 

 (middle) demagnetized; (right) field inward. 



