Isotropic Exchange Integral for Cupric Acetate Monohydrate Crystals

Abstract

MOOKHERJI¹ from his magnetic studies on cupric acetate monohydrate crystal predicted that there is some sort of exchange interaction between adjacent copper atoms. But in the absence of either crystallographic data or diamagnetic dilution data he could not say whether the interaction forces were of Kramers' super-exchange type acting through intermediate oxygen atoms, or whether direct spin interaction occurred. Later, from an examination of anomalous behaviour of cupric acetate monohydrate towards magnetic susceptibility and paramagnetic resonance absorption, Bleaney and Bowers² concluded that there is some form of strong coupling between unpaired electrons on adjacent copper atoms through exchange forces. Van Niekerk and Schoening³ from X-ray analysis showed that cupric acetate monohydrate is a new type of complex having the formula Cu₂(CH₃COO)₄.2H₂O. The Cu-Cu distance is 2.64 Å, showing that there is direct interaction between the copper ions, because the distance for super exchange of Kramers type (Cu-Cu distance) should be of the order of 4 Å. Figgis and Martin⁴ have shown that exchange integral J = l.6 kT_c, where T_c is critical temperature at which Δχ/δT = 0 (χ being the gram molecular susceptibility).