Low-Temperature Magnetic Susceptibility of Ferrous Oxalate Dihydrate

The magnetic susceptibility χₚ of powdered FeC₂{O}₄·2{H}₂O has been measured between 1.3 and 300^∘K. Above ~80^∘K,{{χ}}ₚ=3.40/(T+25.4)$ (cgs/mole). ${{χ}}ₚexhibits a broad, rounded maximum near 30^∘K and a sharp peak at 20^∘K. X-ray structural evidence indicates that{Fe}⁺⁺$ions in this material are linked in chains by oxalate groups. Assuming an antiferromagnetic intrachain exchange constant $J={-}4.9k, it is possible to obtain a reasonable fit of the data above 25^∘K with the susceptibility computed for Ising interactions andS=2$. If the upper maximum is due to chain ordering, the lower maximum then appears to be associated with the cooperative onset of long-range spin order in three dimensions induced by interchain coupling.