Coupling of magnetic ordering and vibrational properties: a density functional theory study of magnetic and structural phase transitions.

A density functional theory (DFT) concept is utilized for a selected class of compounds to propose phase transitions for which the coupling of magnetic ordering and vibrational properties is manifested. The total electronic energies and the phonon spectra are calculated with the same level of accuracy. The total free energy becomes temperature dependent because of the phonon free energy. In particular, the Laves phase compounds ZrMn2 and HfMn2 are studied because they reveal a close competition of phases with different structural properties and different magnetic orderings as a function of temperature. The temperature dependence of the free energy is driven by the entropy of the lattice vibrations, which therefore is responsible for the predicted phase transitions. These ab initio predictions of phase transitions (or indications of peculiar magnetic ground states) are awaiting experimental verification. [ABSTRACT FROM AUTHOR]