Interplay between magnetism and sodium vacancy ordering in NaxCoO2

TL;DR

This study investigates how sodium vacancy arrangements influence magnetic properties in NaxCoO2, revealing temperature-dependent sodium ordering patterns that affect magnetic interactions and ground states.

Contribution

It uncovers the relationship between sodium vacancy ordering and magnetism in NaxCoO2 using nanocalorimetry and x-ray diffraction, highlighting the roles of sodium in magnetic exchange mechanisms.

Findings

Three distinct sodium ordering regimes identified at different temperatures.

Sodium ordering patterns influence magnetic interactions and ground states.

Na intercalation affects electron count and magnetic exchange pathways.

Abstract

Using a combination of low-temperature nanocalorimetry and x-ray diffraction we identify three temperature regimes characterized by distinct Na ordering patterns (low temperature up to 290 K, intermediate 290-340 K, and high above 340 K). Through freezing-in of these patterns we establish the two key roles sodium intercalation plays in the formation of the magnetic ground state: supplying the proper electron count for in-plane ferromagnetic interaction and through the 3D sodium ordering providing the interplane antiferromagnetic exchange path.