Low-Temperature Heat Capacity of $$\hbox {Sr}_2\hbox {Ca}_{12}\hbox {Cu}_{24}\hbox {O}_{41}$$

We report on heat capacity measurements performed on a large \(\hbox {Sr}_{2}\hbox {Ca}_{12}\hbox {Cu}_{24}\hbox {O}_{41}\) single crystal in the temperature range between 0.07 and 20 K and magnetic fields up to 10 T. A transition into the antiferromagnetic ground state is observed at \(T_N = 2.8\) K. The heat capacity becomes strongly time-dependent below 0.5 K due to a Schottky contribution typical for materials with charge or spin-density waves. We found a quasi-linear contribution to the heat capacity that can be attributed to weakly coupled and shifted antiferromagnetic spin chains along the a-direction.