Temperature evolution of itinerant ferromagnetism in SrRuO₃ probed by optical spectroscopy

The temperature (T) dependence of the optical conductivity spectra σ(ω) of a single crystal SrRuO₃ thin film is studied over a T range from 5 to 450 K. We observed significant T dependence of the spectral weights of the charge transfer and interband d-d transitions across the ferromagnetic Curie temperature (T_c∼150 K). Such T dependence was attributed to the increase in the Ru spin moment, which is consistent with the results of density functional theory calculations. T scans of σ(Ω,T) at fixed frequencies Ω reveal a clear T2 dependence below T_c, demonstrating that the Stoner mechanism is involved in the evolution of the electronic structure. In addition, σ(Ω,T) continues to evolve at temperatures above T_c, indicating that the local spin moment persists in the paramagnetic state. This suggests that SrRuO₃ is an intriguing oxide system with itinerant ferromagnetism.