Year: 2015
Type: article
Abstract: Two samples of the ${[\mathrm{C}{\mathrm{a}}_{2}\mathrm{Co}{\mathrm{O}}_{3--t}]}_{0.62}(\mathrm{Co}{\mathrm{O}}_{2})$ misfit cobaltate, often denoted as the $\mathrm{C}{\mathrm{a}}_{3}\mathrm{C}{\mathrm{o}}_{4}{\mathrm{O}}_{9}$ phase, were prepared from the same ceramic material by oxygen and argon annealing, resulting in different carrier concentrations in the conducting $\mathrm{Co}{\mathrm{O}}_{2}$ layers, $n=0.31$ and 0.19 hole/Co, respectively. Electrical and thermal transport properties were studied in dependence of magnetic field up to 140 kOe. The magnetothermopower data reveal an extra spin-entropy contribution to the Seebeck coefficient that is not expected for carriers of Fermi liquid character. Its magnitude is unprecedentedly large and makes at zero field up to $50%$ of the theoretical limit $\frac{{k}_{B}}{|{q}_{e}|}ln2=59\phantom{\rule{0.16em}{0ex}}\ensuremath{\mu}\mathrm{V}/\mathrm{K}$. This spin-entropy contribution is gradually suppressed with increasing magnetic field, and the saturation is even observed when temperatures are low enough. To understand the results, the thermopower is treated in terms of a purely thermodynamic Kelvin formula, and the so-called spin-liquid model is evoked, providing a reason for the spin-entropy manifestation in the ${[\mathrm{C}{\mathrm{a}}_{2}\mathrm{Co}{\mathrm{O}}_{3--t}]}_{0.62}(\mathrm{Co}{\mathrm{O}}_{2})$ misfits.
Source: Physical Review B
Authors: J. Hejtmánek, Z. Jirák, J. Šebek
Language: English
Field: Materials Science
Domain: Physical Sciences
Open Access status: green
OpenAlex ID: W1602164860