Low-temperature heat capacity of the pseudo-one-dimensional magnetic systems CsMn${\mathrm{Cl}}_3$.2${\mathrm{H}}_2$O, $\alpha$-RbMn${\mathrm{Cl}}_3$.2${\mathrm{H}}_2$O, and CsMn${\mathrm{Br}}_3$.2${\mathrm{H}}_2$O

The heat capacity of the isomorphic pseudo-one-dimensional magnetic systems CsMn${\mathrm{Cl}}_3$.2${\mathrm{H}}_2$O, $\alpha$-RbMn${\mathrm{Cl}}_3$.2${\mathrm{H}}_2$O, and CsMn${\mathrm{Br}}_3$.2${\mathrm{H}}_2$O has been analyzed using recently developed estimates for the lattice heat capacity of anisotropic media. The magnetic contribution in the paramagnetic region could be described very well by the $S=\frac{5}{2}$ linear-chain Heisenberg model. The intrachain interaction is found as $\frac{J}{k}=-3.0\mathrm{}$ K for the former two compounds and $\frac{J}{k}=-2.6\mathrm{}$ K for the latter compound. The interchain interactions are smaller by two orders of magnitude. The results, are compared with other experimental evidence. A study of the critical behavior of the magnetic entropy increase yields ${\alpha }^{\prime }=\alpha =+0.10\mathrm{}\pm 0.01$ for all three substances.