The specific heat of tetramethyl ammonium manganese trichloride and its cadmium isomorph is measured for $2<T<\mathrm{}52\mathrm{}$ K. The temperature dependence of the lattice specific heat of the cadmium compound could be fitted with an expression based upon a pseudoelastic approach of the lattice vibrations in this low-dimensional system. Application of this approach to the manganese compound yields a magnetic contribution which fits the overall behavior of a one-dimensional Heisenberg model with an intrachain interaction of $\frac{J}{k}=-6.7\mathrm{}\pm 0.5$ K. Inspection of the low-temperature region yields a satisfactory agreement with the expression $C_m=1.1\left|\frac{\mathrm{kT}}{J}\right|+0.5\mathrm{}{\left|\frac{\mathrm{kT}}{J}\right|}^2-0.13\mathrm{}{\left|\frac{\mathrm{kT}}{J}\right|}^3$, predicted by recent calculations.

• Received 31 July 1975

DOI:https://doi.org/10.1103/PhysRevB.12.5858