Enhanced Seebeck coefficient through the magnetic fluctuations in Sr$_2$Ru$_{1-x}M_x$O$_4$ ($M = $ Co, Mn)

TL;DR

This study investigates how magnetic fluctuations in Co- and Mn-doped Sr$_2$RuO$_4$ influence the Seebeck coefficient, revealing that magnetic fluctuations significantly enhance thermoelectric properties and are linked to non-Fermi-liquid behavior.

Contribution

It provides systematic evidence that magnetic fluctuations in doped Sr$_2$RuO$_4$ enhance the Seebeck coefficient, highlighting the role of magnetic states in thermoelectric performance.

Findings

Magnetic fluctuations correlate with maxima in S/T near magnetic transition temperatures.

Seebeck coefficient increases at low temperatures, indicating non-Fermi-liquid behavior.

Magnetic fluctuations enhance thermoelectric response in Sr$_2$RuO$_4$.

Abstract

The layered perovskite Sr$_2$RuO$_4$ is a most intensively studied superconductor, but its pairing mechanism, which is often coupled intimately with magnetic fluctuations in correlated materials, is still an open question. Here we present a systematic evolution of the Seebeck coefficient in Co- and Mn-substituted Sr$_2$RuO$_4$ single crystals, in which ferromagnetic and antiferromagnetic glassy states respectively emerge in proximity to the superconducting phase of the parent compound. We find that the Seebeck coefficient $S$ divided by temperature $T$, $S/T$, shows a maximum near characteristic temperatures seen in the irreversible magnetization $M_{\rm ir}$ in both of the Co- and Mn-substituted crystals, demonstrating both of the ferromagnetic and antiferromagnetic fluctuations to enhance the Seebeck coefficient. Interestingly, $S/T$ increases with lowering temperature in the parent compound, reminiscent of non-Fermi-liquid behavior, indicating an essential role of coexisting ferromagnetic and antiferromagnetic fluctuations for the itinerant electrons in Sr$_2$RuO$_4$.