Canted antiferromagnetic order in the monoaxial chiral magnets V1/3TaS2 and V1/3NbS2

The Dzyaloshinskii-Moriya (DM) interaction is present in the transition metal dichalcogenides (TMDC) magnets of form ${M}_{1/3}T{\mathrm{S}}_{2}$ ($M=3d$ transition metal, $T\ensuremath{\in}{\mathrm{Nb},\mathrm{Ta}}$), given that the intercalants $M$ form $\sqrt{3}\ifmmode\times\else\texttimes\fi{}\sqrt{3}$ superlattices within the structure of the parent materials $T{\mathrm{S}}_{2}$ and break the centrosymmetry. Competition between DM and ferromagnetic exchange interactions has been shown to stabilize a topological defect known as a chiral soliton in select intercalated TMDCs, initiating interest both in terms of fundamental physics and the potential for technological applications. In the current article we report on our study of the materials ${\mathrm{V}}_{1/3}{\mathrm{TaS}}_{2}$ and ${\mathrm{V}}_{1/3}{\mathrm{NbS}}_{2}$, using a combination of x-ray powder diffraction, magnetization, and single crystal neutron diffraction. Historically identified as ferromagnets, our diffraction results instead reveal that vanadium spins in these compounds are arranged into an A-type antiferromagnetic configuration at low temperatures. Refined moments are 1.37(6) and 1.50(9) ${\ensuremath{\mu}}_{B}$ for ${\mathrm{V}}_{1/3}{\mathrm{TaS}}_{2}$ and ${\mathrm{V}}_{1/3}{\mathrm{NbS}}_{2}$, respectively. Transition temperatures ${T}_{c}=32\phantom{\rule{0.28em}{0ex}}\mathrm{K}$ for ${\mathrm{V}}_{1/3}{\mathrm{TaS}}_{2}$ and 50 K for ${\mathrm{V}}_{1/3}{\mathrm{NbS}}_{2}$ are obtained from the magnetization and neutron diffraction results. We attribute the small net magnetization observed in the low-temperature phases to a subtle ($\ensuremath{\sim}{2}^{\ensuremath{\circ}}$) canting of XY spins in the out-of-plane direction. These new results are indicative of dominant antiferromagnetic exchange interactions between the vanadium moments in adjacent $ab$ planes, likely eliminating the possibility of identifying stable chiral solitons in the current materials.