First-principles study of elastic and phonon properties of the heavy fermion compoundCeMg

Abstract

Elasticity tensor components, Cij, the crystallographic dependence of Poisson’s ratio, the phase stability, and vibrational spectraare computed for nonmagnetic and magnetic CeMg (1:1 Ce:Mg) structures using densityfunctional theory. Results from both the generalized gradient approximation (GGA), and theGGA+U, based upon an effective on-site Coulomb potential,Ueff, are investigated. The GGA low energy structure, with wavevector along [110], disagrees withexperiment, while the [100] structure from experiment is predicted as the 0 K structure in theGGA+U. Accurate estimation of the 20 K Néel temperature can only be achieved with smallUeff,which suggests that CeMg is not a strongly correlated system. For all CeMg structures investigated, wefind C11≈C44; this is consistent with the near equivalency of transverse and longitudinal soundspeeds. The origin of this behavior is the negative stretching force constants forthe interaction between the second- and third-nearest-neighbor Mg and Ce ions,respectively. Results are compared with neutron scattering experiments at 30 and 110 K.