Valence state of Ru at the Mn sites in Pr0.5Sr0.5MnO3:: Thermoelectric power and x-ray absorption near-edge structure spectroscopy

The Ru valence at the Mn sites in Pr0.5Sr0.5MnO3 has been studied using thermoelectric power (TEP) and Ru K- and L-III-edge X-ray absorption near edge structure (XANES) spectroscopy. In comparison with TEP value at 400 K for Pr1-xSrxMnO3 and Pr0.5Sr0.5Mn1-xRuxO3, it was found that the Mn-site doped Ru is in the mixed valence state between 4+ and 5+. Ru K- and L-III-edge XANES study of Pr0.5Sr0.5Mn1-xRuxO3 (x = 0:04 and 0.1) also confirmed the mixed valence state of Ru from the fact that XANES spectrum of the Mn-site doped Ru is in between those of tetravalent and pentavalent ruthenates. These results indicate that the change of carrier density with Ru doping is not sufficient to understand the drastic enhancement of ferromagnetism observed in Ru-doped Pr0.5Sr0.5MnO3. The prime role of Ru is discussed in terms of Mn valence change and magnetic interactions between Mn and doped Ru ions.