The role of La atoms in the formation of a low temperature heat capacity anomaly in La2CuO4, La(2-x)M(x)CuO4 (M = Sr, Ba), and Nd(2-x)La(x)CuO4 cuprates

The low temperature heat capacity of the La2CuO4, La(2-x)M(x)CuO4 (M = Sr, Ba) and Nd(2-x)La(x)CuO4 cuprates has been studied in the temperature range 2-45 K using pulsed differential calorimetry. The residual linear term was found to be well-defined over the entire temperature range with a constant coefficient for each of the compounds. The significant role of the lanthanum atoms is shown to be significant in the formation of the anomaly near 6 meV in the acoustic region of the phonon spectrum of these materials, which is attributed to the characteristics of the interaction of these atoms with their environment. (Author)