Experimental Check of Heisenberg ChainQuantum Statistics for a Ferromagnetic OrganicRadical Crystal

Abstract

One-dimensional quantum statistics has been studied at the limit of isotropic exchange interaction in the unpaired electron system of a ferromagnetic organic radical crystal, 3-(4-chlorophenyl)-1, 5-diphenyl-6-oxoverdazyl. The characteristic field dependence of the magnetic heat capacity of this crystal is quantitatively explained by the theoretical values derived from the Bethe-ansatz technique applied to the quantum transfer matrix, with a unique intrachain exchange constant J/k_B=5.5, K. By the simultaneous measurement of magnetic susceptibility and heat capacity, the three-dimensional ordering at T_c=0.21, K, which is triggered by a weak interchain coupling | zJ'| /k_B=3× 10^-2, K, is confirmed.