Coupling of lattice, spin and intra-configurational excitations of Eu3+ in Eu2ZnIrO6

TL;DR

This study investigates the complex coupling between lattice vibrations, magnetic order, and electronic excitations in Eu2ZnIrO6, revealing strong interactions that influence phonon behavior and electronic transitions across a broad temperature range.

Contribution

It provides a comprehensive analysis of phonon, magnetic, and electronic coupling in Eu2ZnIrO6, highlighting the effects of these interactions on phonon renormalization and electronic mode evolution.

Findings

Phonons show softening and sharpening below ~3TN.

Strong coupling between phonons and magnetic degrees of freedom.

Electronic modes exhibit anomalous temperature behavior and level mixing.

Abstract

In Eu2ZnIrO6, effectively two atoms are active i.e. Ir is magnetically active, which results in complex magnetic ordering within the Ir sublattice at low temperature. On the other hand, although Eu is a van-vleck paramagnet, it is active in the electronic channels involving 4f 6 crystal-field split levels. Phonons, quanta of lattice vibration, involving vibration of atoms in the unit cell, are intimately coupled with both magnetic and electronic degrees of freedom (DoF). Here, we report a comprehensive study focusing on the phonons as well as intra-configurational excitations in double-perovskite Eu2ZnIrO6. Our studies reveal strong coupling of phonons with the underlying magnetic DoF reflected in the renormalization of the phonon self-energy parameters well above the spin-solid phase (TN ~ 12 K) till temperature as high as ~ 3TN, evidences broken spin rotational symmetry deep into the paramagnetic phase. In particular, all the observed first-order phonon modes show softening of varying degree below ~3TN, and low-frequency phonons become sharper, while the high-frequency phonons show broadening attributed to the additional available magnetic damping channels. We also observed a large number of high-energy modes, 39 in total, attributed to the electronic transitions between 4f-levels of the rare-earth Eu3+ ion and these modes shows anomalous temperature evolution as well as mixing of the crystal-field split levels attributed to the strong coupling of electronic and lattice DoF.