Temperature Evolution of Itinerant Ferromagnetism in SrRuO3 Probed by Optical Spectroscopy

The temperature (T) dependence of the optical conductivity spectra sigma(omega) 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 similar to 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 sigma(Omega, T) at fixed frequencies Omega reveal a clear T-2 dependence below T-c, demonstrating that the Stoner mechanism is involved in the evolution of the electronic structure. In addition, sigma(Omega, T) continues to evolve at temperatures above Tc, indicating that the local spin moment persists in the paramagnetic state. This suggests that SrRuO3 is an intriguing oxide system with itinerant ferromagnetism.