Experimental Check of Heisenberg ChainQuantum Statistics for a Ferromagnetic OrganicRadical Crystal

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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 ∣ z J '∣/ k B =3×10 -2 K, is confirmed.