Unconventional magnetic transition and transport behavior in Na0.75CoO2

TL;DR

This study reports an unusual magnetic transition and transport behavior in Na0.75CoO2, revealing a novel electronic state likely due to strong electron correlations, characterized by specific heat, magnetization, resistivity changes, and large magnetoresistance.

Contribution

It identifies a unique magnetic transition and associated electronic phenomena in Na0.75CoO2, highlighting new correlated electronic states in layered cobalt oxides.

Findings

Magnetic transition at Tm ~ 22 K with specific heat jump

Onset of spontaneous magnetization and resistivity kink

Large positive magnetoresistance below Tm

Abstract

Here we report an unconventional magnetic and transport phenomenon in a layered cobalt oxide, NaxCoO2. Only for x = 0.75, a magnetic transition of the second order was clearly detected at Tm ~ 22 K where an apparent specific-heat jump, an onset of extremely small spontaneous magnetization, and a kink in resistivity came in. Moreover large positive magnetoresistance effect was observed below Tm. These features of the transition strongly indicate the appearance of an unusual electronic state that may be attributed to the strongly-correlated electrons in Na0.75CoO2.