Low temperature Schottky anomalies in the specific heat of LaCoO$_{3}$: Defect-stabilized finite spin-states

The nature of the thermally-induced spin-state transition in LaCoO$_{3}$ continues to be a matter of vigorous debate. Recent inelastic neutron spectroscopy studies revealed a thermally excited 0.6 meV excitation associated with this transition, close to earlier electron spin resonance work. We show here that measurement of the low temperature specific heat of LaCoO$_{3}$ single crystals reveals a previously unobserved Schottky anomaly with an energy level splitting, 0.5 meV, associated with the first excited spin-state of the Co$^{3+}$ ion. These states persist well below 2 K and have a $g$-factor around 3.5, consistent with the high-spin spin-orbit triplet, implying the existence of a low density (approximately 0.1 {\%} of the sites) of finite-spin Co ions \textit{even in the T = 0 limit}. We propose that these states are trapped at defects and are consistent with the magnetic excitons observed in earlier work.