The electronic structure and properties of the C15 compounds CeAl₂, LaAl₂ and YAl₂

Results of self-consistent band calculations are reported for the C15 structured XAl₂ materials (X = Y, La, and Ce) using the local spin density functional formalism for assumed ferromagnetic and antiferromagnetic states as well as the paramagnetic state. The X-atoms are found to be the dominant factor is determining the electronic structure near the Fermi energy and this is enhanced by the presence of f-bands close to (LaAl₂) or at (CeAl₂) the Fermi energy. In paramagnetic CeAl₂, the f-bands are about 1 eV wide and, although principally above the Fermi energy, extend down to accomodate the additional electron compared to LaAl₂. The ferromagnetic state is found not to be stable. By contrast, the antiferromagnetic state is found to be stable with a magnetic moment of 0.88μ_B per Ce atom in very good agreement with the maximum moment, 0.89μ_B found in the neutron measurements of Barbara et al. A significant narrowing of the f-bandwidth is observed in the antiferromagnetic state. The antiferromagnetic spin density ordering appears to be related to nesting features in this underlying Fermi surface in LaAl₂ (i.e., no 4f electron) rather than that of CeAl₂.