Nonmagnetic Ground State in RuO₂ Revealed by Muon Spin Rotation

The magnetic ground state of single crystalline RuO₂ was investigated by the muon spin rotation/relaxation (SR) experiment. The spin precession signal due to the spontaneous internal magnetic field B ₋₎₂, which is expected in the magnetically ordered phase, was not observed in the temperature range 5--400~K. Muon sites were evaluated by first-principles calculations using dilute hydrogen simulating muon as pseudo-hydrogen, and B ₋₎₂ was simulated for the antiferromagnetic (AFM) structures with a Ru magnetic moment | m ₑₔ|0. 05B suggested from diffraction experiments. As a result, the possibility was ruled out that muons are localized at sites where B ₋₎₂ accidentally cancels. Conversely, assuming that the slow relaxation observed in SR spectra was part of the precession signal, the upper limit for the magnitude of | m ₑₔ| was estimated to be 4. 8 (2) 10^-4 ₁, which is significantly less than 0. 05B. These results indicate that the AFM order, as reported, is unlikely to exist in the bulk crystal.