FACTORS AFFECTING MAGNETIC QUALITY 



281 



of alloying elements, and values for the metallic and borderline elements are 

 shown in Fig. 31. Most of the values are simply the distances of nearest 

 approach of atoms in the element as it exists in the structure stable at room 

 temperature. Atomic diameter is especially important in theory because the 

 very existence of ferromagnetism is dependent in a critical way on the dis- 

 tance between adjacent atoms. This has been discussed more fully in a 

 previous paper. ^^ 



Even when no phase change occurs in a metal, important changes in struc- 

 ture occur during fabrication and heat treatment, and these are compli- 

 cated and imperfectly understood. When a single crystal is elongated by 

 tension, slip occurs on a limited number of crystal planes that in general 

 are inclined to the axis of tension. As elongation proceeds, the planes on 

 which slip is taking place tend to turn so that they are less inclined to the 

 axis. In this way a definite crystallographic direction approaches parallelism 



(a) ROLLED 



(b) RECRYSTALLIZED 



(C) DRAWN 



Fig. 32 — The preferred orientations of crystals in nickel sheet and wire after fabrication 

 and after recrj-stallization. 



with the length of the specimen. In a similar but more complicated way, 

 any of the usual methods of fabrication cause the many crystals of which it 

 is composed to assume a non-random distribution of orientations, often 

 referred to as preferred or special orientations, or textures. Some of the tex- 

 tures reported for cold rolled and cold drawn magnetic materials are given 

 in Table VI, taken from the compilation by Barrett.''' The orientations of 

 the cubes which are the crystallographic units are shown in Fig. 32 (a) and 

 (c) for cold rolled sheets and cold drawn wires of nickel. 



Since the magnetic properties of single crystals depend on crystallographic 

 direction (anisotropy), the properties of polycrystalline materials in which 

 there is special orientation will also be direction-dependent. In fact it is 

 difficult to achieve isotropy in any fabricated material, even if fabrication 

 involves no more than solidifying from the melt. The relief of the internal 



'3R. M. Bozorth, Bell Sys. Tecli. Jl. 19, 1-39 (1940). 



i-i C. S. Barrett, Structure of Metals, McGraw Hill, New York (1943). 



