Crystal structure and absence of magnetic order in single crystalline RuO$_2$

TL;DR

This study presents detailed structural and magnetic analyses of single-crystalline RuO$_2$, showing it remains a paramagnetic metal with rutile structure down to 2K, contradicting previous claims of antiferromagnetic order.

Contribution

The paper provides comprehensive neutron and X-ray diffraction data demonstrating the absence of magnetic order and structural transitions in RuO$_2$ down to very low temperatures.

Findings

RuO$_2$ remains rutile structure down to 2K

No evidence of magnetic or structural transition between 300K and 2K

Polarized neutron diffraction excludes antiferromagnetic order with moments >0.01 Bohr magnetons

Abstract

RuO$_2$ was considered for a long time to be a paramagnetic metal with an ideal rutile-type structure down to low temperatures, but recent studies on single-crystals claimed evidence for antiferromagnetic order and some symmetry breaking in the crystal structure. We have grown single-crystals of RuO2 by vapor transport using either O$_2$ or TeCl$_4$ as transport medium. These crystals exhibit metallic behavior following a $T^2$ low-temperature relation and a small paramagnetic susceptibility that can be attributed to Pauli paramagnetism. Neither the conductance nor the susceptibility measurements yield any evidence for a magnetic or a structural transition between 300K and $\sim$4 K. Comprehensive single-crystal diffraction studies with neutron and X-ray radiation reveal the rutile structure to persist until 2K in our crystals, and show nearly perfect stoichiometry. Previous observations of symmetry forbidden reflections can be attributed to multiple diffraction. Polarized single-crystal neutron diffraction experiments at 1.6K exclude the proposed antiferromagnetic structures with ordered moments larger than 0.01 Bohr magnetons.