Series of Bulk Magnetic Phase Transitions in NaxCoO2: a muSR study

TL;DR

This muSR study uncovers multiple bulk magnetic phases in NaxCoO2, including a novel phase at x=0.85 with the highest transition temperature, highlighting the complex interplay between magnetic and structural properties.

Contribution

The paper identifies a new magnetic phase at x=0.85 and details the diverse magnetic behaviors across different compositions of NaxCoO2.

Findings

Discovery of a new magnetic phase at x=0.85 with high transition temperature

Observation of a cascade of magnetic transitions in x=0.50 below 85 K

Continuous variation of ordered moments with temperature

Abstract

Using muon spin rotation, well-defined bulk ~ 100% magnetic phases in NaxCoO2 are revealed. A novel magnetic phase is detected for x = 0.85 with the highest transition temperature ever observed for x >= 0.75. This stresses the diversity of x >=0.75 magnetic phases and the link between magnetic and structural degrees of freedom. For the charge-ordered x = 0.50 compound, a cascade of transitions is observed below 85 K. From a detailed analysis of our data, we conclude that the ordered moment varies continuously with temperature and suggest that the two secondary transitions at 48 K and 29 K correspond to a moderate reorientation of antiferromagnetically coupled moments.