Novel Strongly Correlated Europium Superhydrides

TL;DR

This study combines experimental and theoretical methods to discover and analyze novel europium superhydrides under high pressure, revealing their structures, magnetic properties, and stability, with implications for understanding their potential superconductivity.

Contribution

It reports the discovery of new europium superhydrides stabilized at high pressure, detailing their magnetic ordering and structural properties, and highlights the influence of atomic radius on their stability.

Findings

Discovered cubic EuH₉, hexagonal EuH₉, and Eu₈H₄₆ phases.

EuH₉ exhibits antiferromagnetic ordering with T_N up to 24 K.

EuH₉ and Eu₈H₄₆ show ferromagnetic ordering with T_C of 137 K and 336 K.

Abstract

We conducted a joint experimental-theoretical investigation of the high-pressure chemistry of europium polyhydrides at pressures of 86-130 GPa. We discovered several novel magnetic Eu superhydrides stabilized by anharmonic effects: cubic $EuH_{9}$, hexagonal $EuH_{9}$, and an unexpected cubic (Pm-3n) clathrate phase, $Eu_{8}H_{46}$. Monte Carlo simulations indicate that cubic $EuH_{9}$ has antiferromagnetic ordering with T(Neel) up to 24 K, whereas hexagonal $EuH_{9}$ and Pm-3n-$Eu_{8}H_{46}$ possess ferromagnetic ordering with T(Curie) = 137 and 336 K, respectively. The electron-phonon interaction is weak in all studied europium hydrides, and their magnetic ordering excludes s-wave superconductivity, except, perhaps, for distorted pseudohexagonal $EuH_{9}$. The equations of state predicted within the DFT+U approach (the Hubbard corrections were found within linear response theory) are in close agreement with the experimental data. This work shows the great influence of the atomic radius on symmetry-breaking distortions of the crystal structures of superhydrides and on their thermodynamic stability.