Heat capacity investigation of phase separation and spin-state transitions in La$_{1-x}$Sr$_{x}$CoO$_{3}$

We present a heat capacity study (to 0.3 K) on La$_{1-x}$Sr$_{x}$CoO$_{3}$ single crystals (0.00 $<$ x $<$ 0.30). In doped samples we observe three contributions at low $T$; a lattice term ($\propto \quad T^{3})$, an electronic term ($\propto \quad T)$, and a third term proportional to $T^{2}$. Remarkably, the x dependence of the electronic and $T^{2}$ contributions reflects very clearly the known magnetic phase separation, indicating that the $T^{2}$ term is a signature of the non-F matrix. Possible origins related to AF fluctuations will be discussed. At the lowest $T$ the nuclear hyperfine contribution provides a further probe of magnetic order. The electronic contribution also gives the density of states at the Fermi level which, in combination with the hole density from Hall effect, suggests a large effective mass indicative of strong correlations. Finally, the end-member LaCoO$_{3}$ shows a striking Schottky anomaly providing new information on the controversial spin-state transition. In particular, we find further evidence of the around 0.5 meV excitation recently observed by inelastic neutron scattering.