Modified hydrothermal reaction (MHT) for CoV₂O₆·4H₂O nanowire formation and the transformation to CoV₂O₆·2H₂O single-crystals for antiferromagnetic ordering and spin-flop

Abstract

A modified hydrothermal protocol (MHT) has been adopted for the synthesis of a single-crystal of CoV₂O₆·2H₂O. The crystals grew as a result of prolonged hydrothermal reaction between precursor salts of CoCl₂ and ammonium vanadate. At first, the adopted reaction conditions resulted in nanowires of CoV₂O₆·4H₂O. Then with increased reaction time, nanowires changed to single crystals of molecular formula CoV₂O₆·2H₂O. The nanowires have lengths of several tens of micrometers and average diameter of 100 nm. The well defined structure crystallizes in the orthorhombic crystal system having space group Pnma and it displays a = 5.5647(2) Å, b = 10.6870(5) Å, c = 11.8501(5) Å, α = β = γ = 90.00°. Here, each vanadium atom is tetrahedrally connected to four oxygens where two oxygens are connected to vanadium atoms and another two connected to cobalt atoms. Magnetic moment measurement of the nanowires indicates that antiferromagnetic ordering is observed at around 14.9 K and 6.8 K and field induced antiferromagnetic to ferromagnetic (spin-flop-type) transitions have been observed at a low temperature (5–8.8 K) range while these are absent in the as-synthesized single crystals.