title: Direct link between low-temperature magnetism and high-temperature sodium order in NaxCoO2.
abstract: We prove the direct link between low-temperature (T) magnetism and high-T Na+ ordering in NaxCoO2 using the example of a so far unreported magnetic transition at 8 K which involves a weak ferromagnetic moment. The 8 K feature is characterized in detail and its dependence on a diffusive Na+ rearrangement around 200 K is demonstrated. Applying muons as local probes this process is shown to result in a reversible phase separation into distinct magnetic phases that can be controlled by specific cooling protocols. Thus the impact of ordered Na+ Coulomb potential on the CoO2 physics is evidenced opening new ways to experimentally revisit the NaxCoO2 phase diagram.
authors.affiliation: Laboratory for Solid State Physics, ETH Zürich, CH-8093 Zürich, Switzerland. tschulze@phys.ethz.ch
authors.forename: T F
authors.initials: TF
authors.lastname: Schulze
authors.forename: P S
authors.initials: PS
authors.lastname: Häfliger
authors.forename: Ch
authors.initials: Ch
authors.lastname: Niedermayer
authors.forename: K
authors.initials: K
authors.lastname: Mattenberger
authors.forename: S
authors.initials: S
authors.lastname: Bubenhofer
authors.forename: B
authors.initials: B
authors.lastname: Batlogg