Crystal structure and cohesion in ferromagnetic metals of the iron group

Abstract

It is shown that the relationship between type of crystal structure and n (number of outer electrons) valid for transition metals and alloys of the fourth and fifth period, can be extended to ferromagnetic elements and alloys of the iron group if, in the count of n, the unpaired electrons in the majority spin sub-band are neglected. A parameter n _eff (number of effective outer electrons) is thus defined. This property is attributed to the strong anti-bonding character of unpaired electrons and to the interatomic repulsion between electrons having parallel spins. It is also shown that the contrasting behaviour of the cohesive energy of Fe, Co and Ni with respect to homologous elements of the fourth and fifth period, can similarly be ascribed to the difference in the respective numbers of effective outer electrons.