Crystal structure and absence of magnetic order in single-crystalline RuO2

Abstract

RuO2 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 O2 or TeCl4 as transport medium. These crystals exhibit metallic behavior following a T2 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 300 K and ∼4 K. Comprehensive single-crystal diffraction studies with neutron and x-ray radiation reveal the rutile structure to persist until 2 K 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 1.6 K exclude the proposed antiferromagnetic structures with ordered moments larger than 0.01 Bohr magnetons.