Small moments without long-range magnetic ordering in the zero-temperature ground state of the double-perovskite iridate Ba$_2$YIrO$_6$

TL;DR

This study uses advanced computational methods to show that Ba$_2$YIrO$_6$ exhibits small magnetic moments without long-range magnetic order at zero temperature, due to strong quantum fluctuations and frustration effects.

Contribution

It provides a zero-temperature theoretical analysis demonstrating the absence of magnetic order in Ba$_2$YIrO$_6$, challenging previous assumptions of a non-magnetic ground state.

Findings

Ba$_2$YIrO$_6$ has small non-zero magnetic moments at T=0 K.

No magnetic ordering is observed even at zero temperature.

Quantum fluctuations and lattice frustration prevent long-range magnetic order.

Abstract

The spin-orbit coupled double perovskite iridate Ba$_2$YIrO$_6$ with $d^4$ occupancy of Ir is considered as a candidate material for a non-magnetic $J=0$ ground state. The issue of existence of such a state in Ba$_2$YIrO$_6$ however has opened up intense debates both in experimental and theoretical studies. In this study, we revisit the issue using \textit{ab-initio} density functional combined with dynamical mean-field theory to investigate the magnetic properties of Ba$_2$YIrO$_6$ down to zero temperature. To reach the ground state, a recently developed impurity solver based on tensor-product states working directly at zero temperature is employed. We find that Ba$_2$YIrO$_6$ has a small instantaneous non-zero magnetic moment, both at $T=0$ K as well as at room temperature. We did not observe any evidence of magnetic ordering, not even at $T=0$ K. From the calculated local magnetic susceptibility we see that the quantum fluctuations are very strong and effective in screening the instantaneous moments. This dynamical screening, together with frustration effects in the fcc lattice that can lead to almost degenerate magnetic ground states, prevents any long-range ordering.