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

Abstract

RuO₂was 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 RuO₂by vapor transport using either O₂or TeCl₄as transport medium. These crystals exhibit metallic behavior following a<i>T</i>²low-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.