Pressure-induced transitions in RCo5 (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 LaCo5 and YCo5 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 K beta emission spectra. Comparison of theory and experiment confirm for the first time a common feature in both LaCo5 and YCo5 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 LaCo5 was clarified to be caused by the change in the down-spin density of states at the Fermi level.