Magnetic ground state of the frustrated spin-1/2 chain compound $\beta$-TeVO$_4$ at high magnetic fields

TL;DR

This study investigates the magnetic phases of the frustrated spin-1/2 chain compound $eta$-TeVO$_4$ under high magnetic fields, revealing an incommensurate ordered state above 18 T rather than the predicted spin-nematic phase.

Contribution

It provides experimental evidence that the high-field state in $eta$-TeVO$_4$ is an incommensurate magnetic order, challenging the theoretical prediction of a spin-nematic phase in such systems.

Findings

Transition from VC to SDW state occurs at ~3 T along a and c axes.

High-field state above ~18 T is incommensurate magnetic order.

Spin nematic phase is limited to a narrow field range below saturation.

Abstract

Frustrated spin-1/2 chains, despite the apparent simplicity, exhibit remarkably rich phase diagram comprising vector-chiral (VC), spin-density-wave (SDW) and multipolar/spin-nematic phases as a function of the magnetic field. Here we report a study of $\beta$-TeVO$_4$, an archetype of such compounds, based on magnetization and neutron diffraction measurements up to 25 T. We find the transition from the helical VC ground state to the SDW state at $\sim$3 T for the magnetic field along the $a$ and $c$ crystal axes, and at $\sim$9 T for the field along the $b$ axis. The high-field (HF) state, existing above $\sim$18 T, i.e., above $\sim$1/2 of the saturated magnetization, is an incommensurate magnetically ordered state and not the spin-nematic state, as theoretically predicted for the isotropic frustrated spin-1/2 chain. The HF state is likely driven by sizable interchain interactions and symmetric intrachain anisotropies uncovered in previous studies. Consequently, the potential existence of the spin nematic phase in $\beta$-TeVO$_4$ is limited to a narrow field range, i.e., a few tenths of a tesla bellow the saturation of the magnetization, as also found in other frustrated spin-1/2 chain compounds.