72 



BELL SYSTEM TECHNICAL JOURNAL 



Effect of Crystal Structure 



There is another kind of force that must be postulated in order to 

 explain the properties of a single crystal. Because of the spinning 

 electrons which it contains, and also because of their orbital motions, 

 each atom may be regarded as a small magnet. These magnets will 

 influence each other in a purely magnetic way,^'^ just as a group of bar 

 magnets will; and in a crystal it may be readily appreciated that 

 because of these magnetic forces between atoms arranged in a regular 

 fashion, some directions of magnetization are more stable than others. 

 In iron the most stable direction is observed to be that of the cube 

 edge, one of the cubic axes of the crystal. In nickel it is the cube 

 diagonal (Fig. 7). 



25,000 



20,000 



10,000 



400 

 H 



200 

 H 



Fig. 7 — Magnetic properties and crystal structures of single crystals of iron and 

 nickel (Beck, Honda and Kaya, Webster). 



Ordinarily a piece of iron is composed of crystal grains each one of 

 which is too small to be detected by the naked eye. In recent years, 

 however, means have been found to control the grain size of all the 



