Pressure-induced transitions in R Co 5 ( R = Y, La) studied by x-ray emission spectroscopy, x-ray diffraction and density functional theory.

The hydrostatic pressure dependent evolution of the electronic and magnetic structure of LaCo 5 and YCo 5 was investigated by means of x-ray emission spectroscopy, x-ray diffraction, and spin-polarized density functional theory (DFT) calculations. Using experimental lattice parameters the DFT correctly predicts the pressure of the magnetic transition in both compounds to be 26 GPa (La) and 22-23 GPa (Y). The transition was experimentally resolved in the changes of the electronic structure via the integrated absolute difference of the Co Kβ emission spectra. Comparison of theory and experiment confirm for the first time a common feature in both LaCo 5 and YCo 5 to be the source of the transition; the Fermi-level crossing of an up-spin polarized flat band driving the systems into a low spin configuration via a Lifshitz type transition of the Fermi surface. Another phase transition observed around 12 GPa in LaCo 5 was clarified to be caused by the change in the down-spin density of states at the Fermi level.