Singlet ground state in the alternating spin-$1/2$ chain compound NaVOAsO$_4$

TL;DR

This study synthesizes and investigates NaVOAsO$_4$, revealing it as a spin-$1/2$ chain compound with a singlet ground state, a small spin gap, and frustrated interchain couplings, making it promising for high-field experiments.

Contribution

The paper provides detailed experimental and theoretical analysis of NaVOAsO$_4$, identifying its alternating spin-$1/2$ chain structure and quantifying its magnetic properties for the first time.

Findings

Identified the spin gap of approximately 21.4 K.

Confirmed the singlet ground state through NMR measurements.

Demonstrated the compound's potential for high magnetic field studies.

Abstract

We present the synthesis and a detailed investigation of structural and magnetic properties of polycrystalline NaVOAsO$_4$ by means of x-ray diffraction, magnetization, electron spin resonance (ESR), and $^{75}$As nuclear magnetic resonance (NMR) measurements as well as density-functional band structure calculations. Temperature-dependent magnetic susceptibility, ESR intensity, and NMR line shift could be described well using an alternating spin-$1/2$ chain model with the exchange coupling $J/k_{\rm B}\simeq 52$ K and an alternation parameter $\alpha \simeq 0.65$. From the high-field magnetic isotherm measured at $T=1.5 $ K, the critical field of the gap closing is found to be $ H_{\rm c}\simeq 16$ T, which corresponds to the zero-field spin gap of $\Delta_0/k_{\rm B}\simeq 21.4$ K. Both NMR shift and spin-lattice relaxation rate show an activated behavior at low temperatures, further confirming the singlet ground state. The spin chains do not coincide with the structural chains, whereas the couplings between the spin chains are frustrated. Because of a relatively small spin gap, NaVOAsO$_4$ is a promising compound for further experimental studies under high magnetic fields.