Pressure-induced Frustration of Magnetic Coupling in Elemental Europium

TL;DR

This paper investigates how high pressure suppresses magnetic order in elemental europium, revealing a frustrated magnetic state that transitions into superconductivity, and discusses its implications within various theoretical frameworks.

Contribution

It provides a detailed first-principles analysis of pressure-induced magnetic frustration and its connection to superconductivity in europium, highlighting a novel frustrated magnetic phase.

Findings

Magnetic exchange constants vanish near 82 GPa

Eu $4f^7$ moment remains unchanged at high pressure

Superconductivity observed at T$_c$=1.7K

Abstract

Applying linear response and the magnetic force theorem in correlated density functional theory, the inter-sublattice exchange constants of antiferromagnetic Eu are calculated and found to vanish near the pressure of P$_c$=82 GPa, just where magnetic order is observed experimentally to be lost. The Eu $4f^7$ moment remains unchanged at high pressure, again in agreement with spectroscopic measurements, leaving the picture of perfect frustration of interatomic Ruderman-Kittel-Kasuya-Yoshida couplings in a broad metallic background, leaving a state of electrons strongly exchange coupled to arbitrarily oriented, possibly quasistatic local moments. This strongly frustrated state gives way to superconductivity at T$_c$=1.7K, observed experimentally. These phenomena, and free energy considerations related to correlations, suggest an unusual phase of matter that is discussed within the scenarios of the Doniach Kondo lattice phase diagram, the metallic spin glass class, and itinerant spin liquid or spin gas systems.