Non-collinear Order and Spin-Orbit Coupling in Sr$_3$ZnIrO$_6$

TL;DR

This study reveals that Sr$_3$ZnIrO$_6$ exhibits a non-collinear antiferromagnetic order below 17 K driven by strong spin-orbit coupling, with detailed experimental and theoretical analysis of its magnetic structure and excitations.

Contribution

It provides the first comprehensive experimental and theoretical characterization of the non-collinear magnetic order in Sr$_3$ZnIrO$_6$ driven by spin-orbit coupling.

Findings

Transition at 17 K to 3D antiferromagnetic order

Observation of spin wave spectrum with zone boundary at ~5 meV

Non-collinear magnetic structure explained by anisotropic exchange

Abstract

Sr$_{3}$ZnIrO$_{6}$ is an effective spin one-half Mott insulating iridate belonging to a family of magnets which includes a number of quasi-one dimensional systems as well as materials exhibiting three dimensional order. Here we present the results of an extensive investigation into the magnetism including heat capacity, a.c. susceptibility, muon spin rotation ($\mu$SR), neutron diffraction and inelastic neutron scattering on the same sample. It is established that the material exhibits a transition at about $17$ K into a three-dimensional antiferromagnetic structure with propagation vector $\boldsymbol{k}=(0,\frac{1}{2},1)$ in the hexagonal setting of R$\bar{3}$c and non-collinear moments of $0.87$$\mu_B$ on Ir$^{4+}$ ions. Further we have observed a well defined powder averaged spin wave spectrum with zone boundary energy of $\sim 5$ meV at $5$ K. We stress that a theoretical analysis shows that the observed non-collinear magnetic structure arises from anisotropic inter- and intra- chain exchange which has its origin in significant spin-orbit coupling. The model can satisfactorily explain the observed spin wave excitations.