Novel Strongly Correlated Europium Superhydrides

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 EuH9, hexagonal EuH9, and an unexpected cubic (Pm (3) over barn) clathrate phase, Eu8H46. Monte Carlo simulations indicate that cubic EuH9 has antiferromagnetic ordering with T-N of up to 24 K, whereas hexagonal EuH9 and Pm (3) over barn-Eu8H46 possess ferromagnetic ordering with T-C = 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 EuH9. The equations of state predicted within the DFT+U approach (U - J 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.

Automated summary

A joint experimental-theoretical investigation revealed novel magnetic Eu superhydrides with distinct magnetic orderings and phase transitions. The study showed that the atomic radius plays a significant role in the symmetry-breaking distortions and thermodynamic stability of superhydrides, as evidenced by close agreement between experimental data and predictions based on the DFT+U approach.