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

TL;DR

This study investigates the electronic structure of non-centrosymmetric EuTGe3 compounds with various transition metals using hard x-ray photoelectron spectroscopy, revealing stable Eu2+ valence and changes in Ge-T bonding with different metals.

Contribution

It provides the first detailed bulk electronic structure analysis of EuTGe3 compounds with different transition metals, confirming Eu2+ valence stability and analyzing bonding variations.

Findings

Eu 3d core level confirms Eu2+ valence with minor Eu3+ contribution.

Ge 2p spectrum shifts indicate changing Ge-T bonding strength.

Valence band structures match ab initio calculations.

Abstract

Non-centrosymmetric EuTGe3 (T=Co, Ni, Rh, and Ir) possesses magnetic Eu2+ 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 EuTGe3 (T=Co, Ni, Rh, and Ir) by hard x-ray photoelectron spectroscopy. The Eu 3d core level spectrum confirms the robust Eu2+ valence state against the transition metal substitution with a small contribution from Eu3+. 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.