Electronic structure and magnetism of amorphousCo1−xBxalloys

The electronic structure of amorphous ${\mathrm{Co}}_{1\mathrm{-}\mathit{x}}$ ${\mathrm{B}}_{\mathit{x}}$ (x=0.17, 0.23, and 0.32) alloys were calculated to clarify their magnetism and electronic specific heat. The electronic structures were calculated self-consistently, both in the spin-polarized and paramagnetic states, by employing the most-localized linear muffin-tin orbital method together with the recursion method. B s and p states split into bonding and antibonding states, and B p states, in particular, hybridize with the tails of Co d states. The exchange splitting of Co d states decreases with increasing B content mainly because of the enhancement of the hybridization. As a result, amorphous Co-B alloys become less ferromagnetic as their B content increases. The calculated magnetic moments per Co atom are proportional to the exchange splitting of Co d states, and decrease with increasing B content. They can be satisfactorily explained by the generalized Stoner model, and agree quantitatively with the experimental data. The density of states at the Fermi level rises with increasing B content, because the highest peak of the minority Co d states shifts toward the Fermi level owing to the decrease in the exchange splitting. This explains a gradual increase in the electronic specific coefficient observed in the experiment.