Helicoidal magnetic order in a clean copper oxide spin chain compound

TL;DR

This study reveals a helicoidal magnetic order in the clean copper oxide compound NaCu$_2$O$_2$, demonstrating that such order can occur intrinsically without impurity effects, supported by experimental measurements and theoretical modeling.

Contribution

It provides the first clear evidence of intrinsic helicoidal magnetic order in NaCu$_2$O$_2$, distinguishing it from impurity-induced effects seen in similar compounds.

Findings

NaCu$_2$O$_2$ exhibits long-range incommensurate magnetic helix below 13 K

Substitutional disorder is negligible, ruling out impurity-induced helix

A frustrated spin Hamiltonian accurately describes the magnetic behavior

Abstract

We report susceptibility, specific heat, and neutron diffraction measurements on NaCu$_2$O$_2$, a spin-1/2 chain compound isostructural to LiCu$_2$O$_2$, which has been extensively investigated. Below 13 K, we find a long-range ordered, incommensurate magnetic helix state with a propagation vector similar to that of LiCu$_2$O$_2$. In contrast to the Li analogue, substitutional disorder is negligible in NaCu$_2$O$_2$. We can thus rule out that the helix is induced by impurities, as was claimed on the basis of prior work on LiCu$_2$O$_2$. A spin Hamiltonian with frustrated longer-range exchange interactions provides a good description of both the ordered state and the paramagnetic susceptibility.