Magnetic and charge transport properties of the Na-based Os oxide pyrochlore

TL;DR

This study reports the synthesis and characterization of a novel Na-based osmium oxide pyrochlore, revealing its structure, transport, and magnetic properties, including the absence of superconductivity and the presence of a magnetic anomaly.

Contribution

It is the first synthesis of Na-based osmium oxide pyrochlore via ion-exchange, with detailed structural and physical property analysis.

Findings

Confirmed defect-type pyrochlore structure with composition Na1.4Os2O6.H2O.

No superconductivity observed above 2 K.

Detected magnetic anomaly at ~57 K and magnetoresistance effects.

Abstract

Na-based osmium oxide pyrochlore was synthesized for the first time by an ion-exchange method. KOs2O6 was used as a host compound. Elelectron probe micro-analysis, synchrotron x-ray diffraction analysis, and thermo-gravimetric analysis confirmed its structure not as the beta-type but as the defect-type pyrochlore. The composition was identified as Na1.4Os2O6.H2O. Electrical resistivity, heat capacity, and magnetization measurements of the polycrystalline Na1.4Os2O6.H2O clarified absence of superconductivity above 2 K, being in contrast to what were found for the beta-pyrochlore AOs2O6 (A = Cs, Rb, K). Sommerfeld coefficient of 22 mJ K-2 mol-1 of Na1.4Os2O6.H2O was smallest among those of AOs2O6. A magnetic anomaly at ~57 K and possible associated magnetoresistance (+3.7 % at 2 K in 70 kOe) were found.