Variation of Exchange IntegralJwith Lattice Spacing from Specific-Heat Measurements on Linear-Chain Antiferromagnets

The specific heat of the copper tetrammine salt Cu${\left(\mathrm{N}{\mathrm{H}}_3\right)}_4$S${\mathrm{O}}_4$ · N${\mathrm{H}}_3$ has been fitted to the Bonner-Fisher theory for linear magnetic chains of spin ½ and with isotropic nearest-neighbor interaction, in the range 1-20 K. The exchange constant is $J=2.96\mathrm{}\pm 0.02$ K. The results are compared with other similar linear-magnetic-chain copper salts to further confirm the simple power-law dependence of exchange interaction versus interionic spacing.