Magnetic Ordering in VF2

Abstract

The compound VF₂ has been prepared by treatment of vanadium metal with HF gas at 1250°C to form VF₃, and subsequent reduction to VF₂ at 1150°C with a controlled mixture of HF and H₂. Debye—Scherrer photographs show VF₂ to have the rutile structure, isomorphic with MnF₂, FeF₂, CoF₂, NiF₂, and ZnF₂. Heat‐capacity measurements from room temperature to 5°K, using a platinum resistance thermometer, show a peak in heat capacity at 7.0°K, presumably associated with long‐range magnetic ordering, and a large magnetic contribution to the heat capacity at higher temperatures. The major fraction of the magnetic entropy of Rln4 is acquired in the short‐range‐order region. The behavior of the magnetic entropy is similar to that found in CuCl₂ and CrCl₂ where there is extensive short‐range magnetic ordering in one‐dimensional chains of metal atoms coupled by relatively strong exchange forces. This suggests that in VF₂, unlike the other iron group fluorides, the strong exchange interactions are between neighboring vanadium atoms which form one‐dimensional chains parallel to the tetragonal axis and that the exchange forces between a vanadium atom and its eight nearest neighbors in 〈111〉 directions are relatively weak.