One-Dimensional Quantum Magnetism in the S = 1/2 Mo(V) system, KMoOP2O7

TL;DR

This study combines experimental and computational methods to demonstrate that KMoOP$_2$O$_7$ is a realization of the $S=1/2$ Heisenberg chain antiferromagnet, showing one-dimensional magnetic correlations and very weak long-range order.

Contribution

It provides a detailed characterization of KMoOP$_2$O$_7$ as a new quantum magnet with one-dimensional $S=1/2$ chains, supported by neutron scattering, magnetometry, and ab-initio calculations.

Findings

KMoOP$_2$O$_7$ exhibits $S=1/2$ Heisenberg chain antiferromagnet behavior.

Long-range magnetic order appears below 0.54 K with a very small ordered moment.

Exchange interactions are approximately $J_1 eq 0$ and $J_2 eq 0$, confirming one-dimensional magnetic correlations.

Abstract

We present a comprehensive experimental and ab-initio study of the $S=1/2$ Mo$^{5+}$ system, KMoOP$_2$O$_7$, and show that it realizes the $S = 1/2$ Heisenberg chain antiferromagnet model. Powder neutron diffraction reveals that KMoOP$_2$O$_7$ forms a magnetic network comprised of pairs of Mo$^{5+}$ chains within its monoclinic $P2_1/n$ structure. Antiferromagnetic interactions within the Mo$^{5+}$ chains are identified through magnetometry measurements and confirmed by analysis of the magnetic specific heat. The latter reveals a broad feature centred on $T_\textrm{N} = 0.54$ K, which we ascribe to the onset of long-range antiferromagnetic order. No magnetic Bragg scattering is observed in powder neutron diffraction data collected at 0.05 K, however, which is consistent with a strongly suppressed ordered moment with an upper limit $\mu_\textrm{ord} < 0.15 \mu_\textrm{B}$. The one-dimensional character of the magnetic correlations in KMoOP$_2$O$_7$ is verified through analysis of inelastic neutron scattering data, resulting in a model with $J_\textrm{1} \approx 34$ K and $J_\textrm{2} \approx -2$ K for the intrachain and interchain exchange interactions, respectively. The origin of these experimental findings are addressed through density-functional theory calculations.