Magnetic structure of the zigzag chain familyNaxCa1−xV2O4determined by muon-spin rotation

Abstract

We present muon-spin-rotation measurements on polycrystalline samples of the complete family of the antiferromagnetic (AF) zigzag chain compounds, ${\text{Na}}_{x}{\text{Ca}}_{1\ensuremath{-}x}{\text{V}}_{2}{\text{O}}_{4}$. In this family, we explore the magnetic properties from the metallic ${\text{NaV}}_{2}{\text{O}}_{4}$ to the insulating ${\text{CaV}}_{2}{\text{O}}_{4}$. We find a critical ${x}_{c}(\ensuremath{\sim}0.833)$ which separates the low and high Na-concentration-dependent transition temperature and its magnetic ground state. In the $x<{x}_{c}$ compounds, the magnetic ordered phase is characterized by a single homogenous phase and the formation of incommensurate spin-density-wave order. Whereas in the $x>{x}_{c}$ compounds, multiple subphases appear with temperature and $x$. Based on the muon data obtained in zero external magnetic field, a careful dipolar field simulation was able to reproduce the muon behavior and indicates a modulated helical incommensurate spin structure of the metallic AF phase. The incommensurate modulation period obtained by the simulation agrees with that determined by neutron diffraction.