Research Highlight

Anisotropic exchange interactions in the ferromagnetic quantum critical material CeRh₆Ge₄

The 4f-electron compound CeRh₆Ge₄ exhibits ferromagnetism at low temperatures. By applying the external pressure, the ferromagnetic transition temperature decreases toward absolute zero, showing a “quantum critical phenomenon.” A quantum critical phenomenon refers to a regime where quantum fluctuations strongly influence the physical properties. However, observing such behavior in a ferromagnet is considered unusual, because in most cases applying pressure enhances quantum fluctuations to destroy ferromagnetism. The question is why CeRh₆Ge₄ can exhibit a quantum critical phenomenon.

We investigated ferromagnetic fluctuations in CeRh₆Ge₄ using dynamical mean-field theory (DMFT). As a result, we successfully reproduced the ferromagnetism by localized 4f electrons. Furthermore, we found that the interactions between 4f electrons that drive ferromagnetism possess strong anisotropy. When spin interactions are anisotropic, it is known that ferromagnetism can remain robust even under strong quantum fluctuations. Thus, we concluded that this anisotropic interaction stabilizes ferromagnetism and consequently allows the material to realize a quantum critical phenomenon in CeRh₆Ge₄.

S. Itokazu, A. Kirikoshi, H. O. Jeschke, J. Otsuki
Comm. Mater. 6, 269 (2025)－Published 25 November, 2025