Dome-shaped magnetic phase diagram of thermoelectric layered cobaltites

TL;DR

This study reveals a dome-shaped relationship between magnetic transition temperature and composition in layered cobaltites, explained by a Hubbard model on a 2D triangular lattice, highlighting a common low-temperature magnetic state.

Contribution

It demonstrates a universal dome-shaped magnetic phase diagram across different layered cobaltites using muon spin spectroscopy and theoretical modeling.

Findings

Magnetic transition temperature varies dome-shaped with composition.

A common low-temperature magnetic state is observed across cobaltite types.

The behavior is explained by the Hubbard model on a 2D triangular lattice.

Abstract

Using muon spin spectroscopy we have found that, for both Na$_x$CoO$_2$ (0.6 $\leq x \leq$ 0.9) and 3- and 4-layer cobaltites, a common low temperature magnetic state (which in some cases is manifest as an incommensurate spin density wave) forms in the CoO$_2$ planes. Here we summarize those results and report a dome-shaped relation between the transition temperature into the low-$T$ magnetic state and the composition $x$ for Na$_x$CoO$_2$ and/or the high-temperature asymptotic limit of thermopower in the more complex 3- and 4-layer cobaltites. This behavior is explained using the Hubbard model on two-dimensional triangular lattice in the CoO$_2$ plane.