New Evidence for a Low-Temperature Magnetic Ground State in Double-Perovskite Iridates with Ir5+(5d4) Ions

TL;DR

This study reveals a delicate magnetic order below 1.7 K in double-perovskite iridates with Ir5+ ions, challenging the conventional Jeff=0 singlet ground state model and highlighting complex interaction effects.

Contribution

It provides new experimental evidence of magnetic order in Ba2YIrO6 and doped variants, suggesting a competing interplay of spin-orbit coupling and Hund's coupling.

Findings

Magnetic order confirmed below 1.7 K

Contradicts the Jeff=0 singlet ground state model

Highlights complex interplay of interactions

Abstract

We report an unusual magnetic ground state in single-crystal, double-perovskite Ba2YIrO6 and Sr doped Ba2YIrO6 with Ir5+(5d4) ions. Long-range magnetic order below 1.7 K is confirmed by DC magnetization, AC magnetic susceptibility and heat capacity measurements. The observed magnetic order is extraordinarily delicate and cannot be explained in terms of either a low-spin S=1 state, or a singlet Jeff=0 state imposed by the spin-orbit interactions (SOI). Alternatively, the magnetic ground state appears consistent with a SOI that competes with comparable Hund's rule coupling and inherently large electron hopping, which cannot stabilize the singlet Jeff=0 ground state. However, this picture is controversial, and conflicting magnetic behavior for these materials is reported in both experimental and theoretical studies, which highlights the intricate interplay of interactions that determine the ground state of materials with strong SOI.