Ab initiostudy of structural, magnetic, vibrational, and thermodynamic properties of the Laves-phase compoundHfMn2

Abstract

By an ab initio density functional approach, structural, magnetic, vibrational, and thermodynamic properties of $\mathrm{Hf}{\mathrm{Mn}}_{2}$ were studied. These properties were derived for the $C14$, $C15$, and $C36$ crystal structures, revealing a close energetical competition between the ferromagnetically ordered phases and the antiferromagnetic $C14$ phase ($C14$ AF). Based on ab initio calculations of phonon densities of states, temperature dependent free energies were derived for each of the nonmagnetic, ferromagnetic, and the $C14$ AF phases. From the comparison of free energies, it is deduced that at temperatures below ${T}_{c}=230\phantom{\rule{0.3em}{0ex}}\mathrm{K}$, the ferromagnetic $C14$ phase is the ground state, whereas above ${T}_{c}$, $C14$ AF is stabilized because of the vibrational entropies. This predicted transition would indicate a dynamical change of long range magnetic ordering.