Itinerant Antiferromagnetism in RuO_{2}

Area of Science:

• Condensed matter physics
• Materials science
• Solid-state chemistry

Background:

• Bulk rutile RuO2 has been traditionally characterized as a Pauli paramagnet.
• Understanding the magnetic properties of transition metal oxides is crucial for developing new electronic materials.

Purpose of the Study:

• To investigate the magnetic and structural properties of rutile RuO2 at lower temperatures.
• To identify any previously undetected magnetic ordering or phase transitions.

Main Methods:

• Polarized neutron diffraction was employed to probe magnetic ordering.
• Density functional theory plus U (DFT+U) calculations were performed to model electronic structure and magnetic interactions.

Main Results:

• A hitherto undetected lattice distortion in RuO2 below approximately 900 K.
• Antiferromagnetic order was observed up to at least 300 K, with a small room temperature magnetic moment of ~0.05 μB.
• DFT+U calculations suggest antiferromagnetism is favored due to a Fermi surface instability, even for small Hubbard U values (~1 eV).

Conclusions:

• Rutile RuO2 exhibits antiferromagnetic ordering below 900 K, contrary to previous assumptions of Pauli paramagnetism.
• The observed high Néel temperature and small itinerant moments make RuO2 a unique material among ruthenates and oxides.
• The findings open new avenues for exploring RuO2 in spintronic and magnetic applications.