MAGNETIZATION IN CRYSTALS — DILLON 



393 



UP 



DOWN 



Figure 4. — Key to plate 3 showing the direction of the magnetization in each of the domains. 



The discrete regions in each one of which the magnetization is 

 directed in a distinct direction are called domains. The transitions 

 between adjacent domains are called domain walls. 



Many years ago the concept of domains was put forth by the French 

 physicist Pierre Weiss [11] to account for the puzzling behavior 

 of magnetic materials. The facts were these : A piece of a ferromag- 

 netic material in the absence of an externally applied magnetic field 

 showed no magnetic moment. However, the application of a rela- 

 tively small field seemed to induce a very large moment. Applica- 

 tion of fields above some "saturating" value seemed to have no fur- 

 ther effect. Weiss proposed that the material was broken up into 

 "domains" in each of which the material had its maximum magneti- 

 zation for the temperature prevailing. He suggested that large in- 

 ternal "molecular fields" kept the magnetization alined within the 

 domains. The application of magnetic fields was thought to cause 



