Energy-band analysis of ordered Fe and Co compounds: Implications for amorphous ferromagnets

Earlier work has shown that global properties of alloys, such as the magnetization per unit cell, are most easily understood in terms of global parameters like the total number of valence electrons and the average "magnetic valence." Here, energy-band calculations are used to show how such global properties relate to site-resolved properties, such as the charge on individual atoms. The calculations show that alloys of Fe and Co with early-transition-metal solutes can be characterized as "split-band" systems (approximately separate sets of $d$ bands; one containing primarily host states, the other primarily solute states). The energy-band calculations exhibit systematic variation of the electronic structure with the Periodic-Table position of the solute. A particularly interesting result is the remarkable constancy of the number of $d$ electrons on the host atoms, in the face of substantial changes in other aspects of the electronic structure. The relevance of calculations for ordered compounds to amorphous alloys is discussed in some detail. In short, although amorphous structures differ in many ways, the effects of these differences tend to cancel, making calculations for ordered compounds a good guide to experimental magnetic trends in the corresponding amorphous alloys.