Research Highlight

Frustrated magnetism induced by orbital ordering in alkali superoxides

Alkali superoxides AO₂ (A = Na, K, Rb, Cs) are strongly correlated materials in which the oxygen molecular ion O₂⁻ possesses both spin and orbital degrees of freedom. Among them, CsO₂ is known to exhibit a rapid enhancement of magnetic correlations below 70 K, but the origin of this behavior has remained unclear. We constructed an effective model based on the energy bands obtained from first-principles calculations and analyzed its magnetic properties. As a result, we revealed that at low temperatures an “orbital order,” in which the orbital arrangement becomes aligned, emerges, and that this ordering significantly enhances the geometric frustration of the spins.

Several materials have been known in which orbital order simplifies the connectivity of spins, effectively leading to a “one-dimensional” magnetic network. However, it is extremely rare cases that orbital order instead makes the spin network more complicated. In this study, we pointed out for the first time that CsO₂ may belong to this uncommon category.

The paper reporting these findings was selected as an Editors’ Suggestion in Physical Review B, published by the American Physical Society.

K. Shibata, M. Naka, H. O. Jeschke, J. Otsuki
Phys. Rev. B 109, 235115 (2024) －Published 7 June 2024