Spin liquid behavior of a three-dimensional magnetic system Ba$_3$NiIr$_2$O$_9$ with $S$ = 1

TL;DR

This study reports the discovery of a three-dimensional quantum spin liquid state in Ba$_3$NiIr$_2$O$_9$, a high-spin system with complex magnetic interactions, demonstrating a rare example of 3D QSL with $S=1$.

Contribution

The paper introduces a novel 3D high-spin quantum spin liquid material using transition metal ions at inequivalent sites, expanding the understanding of QSL in higher dimensions and spins.

Findings

Ba$_3$NiIr$_2$O$_9$ exhibits gapless QSL behavior down to 100 mK.

Strong magnetic exchange interactions between Ir and Ni sublattices.

Dynamically fluctuating magnetic moments on both sublattices.

Abstract

The quantum spin liquid (QSL) is an exotic phase of magnetic materials where the spins continue to fluctuate without any symmetry breaking down to zero temperature. Among the handful reports of QSL with spin $S\ge$1, examples with magnetic ions on a three-dimensional magnetic lattice are extremely rare since both larger spin and higher dimension tend to suppress quantum fluctuations. In this work, we offer a new strategy to achieve 3-D QSL with high spin by utilizing two types of transition metal ions, both are magnetically active but located at crystallographically inequivalent positions. We design a 3-D magnetic system Ba$_3$NiIr$_2$O$_9$ consisting of interconnected corner shared NiO$_6$ octahedra and face shared Ir$_2$O$_9$ dimer, both having triangular arrangements in \textit{a-b} plane. X-ray absorption spectroscopy measurements confirm the presence of Ni$^{2+}$ ($S$=1). Our detailed thermodynamic and magnetic measurements reveal that this compound is a realization of gapless QSL state down to at least 100 mK. Ab-initio calculations find a strong magnetic exchange between Ir and Ni sublattices and in-plane antiferromagnetic coupling between the dimers, resulting in dynamically fluctuating magnetic moments on both the Ir and Ni sublattice.