Magnetostructural properties of RCo$_{2}$ (R = rare earth) compounds

First principles electronic structure calculations show that the cubic Laves phase (C15) is stable for GdCo$_{2}$ and TbCo$_{2}$, while the ground state structures of DyCo$_{2}$, HoCo$_{2}$, and ErCo$_{2}$ are tetragonal distortions of the cubic C15, orthorhombic, and rhombohedral structures, respectively. The R and Co moments exhibit antiparallel coupling, forming a ferrimagnetic state in every ground state structure of RCo$_{2}$. The predicted magnetostructural properties of RCo$_{2}$ are in good agreement with x-ray powder diffraction and magnetic measurements. The spin splitting of the conduction electrons due to the indirect R-R exchange plays a crucial role in the magnetostructural transformations in the R = Dy, Ho, and Er RCo$_{2}$ phases, and accounts for its absence in the monomorphic GdCo$_{2}$ and TbCo$_{2}$ compounds.