Bulk electronic structure of non-centrosymmetric EuTGe3 ( T=Co , Ni, Rh, Ir) studied by hard x-ray photoelectron spectroscopy

Abstract

Non-centrosymmetric EuT Ge3 (T =Co, Ni, Rh, and Ir) possesses magnetic Eu 2+ ions and antiferromagnetic ordering appears at low temperatures. Transition metal substitution leads to changes of the unit cell volume and of the magnetic ordering. However, the magnetic ordering temperature does not scale with the volume change and the Eu valence is expected to remain divalent. Here we study the bulk electronic structure of non-centrosymmetric EuT Ge3 (T =Co, Ni, Rh, and Ir) by hard x-ray photoelectron spectroscopy. The Eu 3d core level spectrum confirms the robust Eu 2+ valence state against the transition metal substitution with a small contribution from Eu 3+ . The estimated Eu mean-valence is around 2.1 in these compounds as confirmed by multiplet calculations. In contrast, the Ge 2p spectrum shifts to higher binding energy upon changing the transition metal from 3d to 4d to 5d elements, hinting of a change in the Ge-T bonding strength. The valence bands of the different compounds are found to be well reproduced by ab initio band structure calculations.

Pressure evolution of the electronic structure of non-centrosymmetric EuRhGe3

“…Figure 3 shows the simulated partial DOS that mainly contribute to the valence band and their sum at 0, 20, and 43 GPa. The simulated DOS at ambient pressure is consistent with the previous result [27]. The Eu 4f orbitals are almost half occupied and the 4f DOS is localized at −1 eV.…”

“…The obtained v is plotted in figure 2(b) as a function of pressure. The Eu valence obtained at ambient pressure is 2.13 ± 0.02 which is similar to the value obtained in the earlier photoelectron spectroscopy (PES) experiment [27]. With increasing pressure up to 20 GPa, v linearly increases, and at higher pressures shows a tendency towards saturation.…”

“…The Hubbard interaction was taken into account by using a simplified scheme of DFT + U [37]. The Hubbard interaction U for Eu was assumed to be 3.8 eV in order to match the Eu 4f peak position observed in the PES experiment [27]. The U value was fixed to a constant throughout the whole pressure region.…”

Magnetic properties of the noncentrosymmetric tetragonal antiferromagnet EuPtSi$_{3}$

“…A candidate for such behavior is EuPtSi 3 , belonging to a class of europium-based compounds crystallizing in the noncentrosymmetric tetragonal space group I4mm [19][20][21][22][23][24][25][26][27][28][29][30][31][32]. In a seminal study, Kumar and colleagues investigated single-crystal platelets grown from a tin solution [33].…”

HAXPES for Materials Science at the GALAXIES Beamline

“…HAXPES at GALAXIES has been used both for fundamental studies (e.g in semiconductors, oxides [5], topological insulator [6] or heavy fermion compounds [7]) and applied science. The large penetration depth of the electrons at high kinetic energy makes HAXPES an ideal tool for depth profiling.…”