THE PHYSICAL BASIS OF FERROMAGNETISM 



23 



indicates that some of the outer electrons of platinum go into the M 

 band of nickel, but that they do not fill this level as rapidly as the 

 outer electrons of copper do when this element is added. 



Electron shells that are completely filled behave more like hard elastic 

 spheres than those which are only partially filled. In solid copper with 



15 20 25 30 35 40 45 50 55 



ATOMIC PER CENT OF ELEMENT ADDED TO NICKEL 



65 70 



Fig. 13 — The saturation magnetization of nickel decreases upon the addition of 

 other elements having 1,2,3, ... electrons in the outermost shell. 



a complete 3d shell and a 4^ shell just begun, the 4^ electrons "overlap " 

 those of neighboring atoms so much that their connection with any one 

 atom is lost; the 2)d shells on the other hand have very little overlap 

 with neighboring atoms. In the ferromagnetic metals the d)d shells 

 are incomplete and the overlap is greater than in copper; this affects 

 the interaction responsible for the Weiss molecular field, now to be 



