Nuclear magnetic resonance and magnetization studies of the ferromagnetic ordering temperature suppression in Ru deficient SrRuO3

The synthesis of SrRuO3 under high-pressure oxygen produces a nonstoichiometric form with randomly distributed vacancies on the Ru sites, along with a significantly reduced ferromagnetic ordering temperature. In order to gain additional insight into the suppression of the ferromagnetism, local studies utilizing Ru-99.101 zero-field spin-echo NMR, Ru K-edge XAFS and XANES, along with complimentary magnetization and X-ray diffraction measurements, have been carried out on samples of SrRuO3 annealed at both (ambient) atmospheric pressure and 'high-pressure' oxygen (600 atm). Consistent with previous work, the NMR spectrum for ambient SrRuO3 consists of two well-defined peaks at 64.4 and 72.2 MHz corresponding to the Ru-99 and Ru-101 isotopes, respectively, and a hyperfine field of 329 kG. Although the magnetization measurements show a lower ferromagnetic ordering temperature for the high-pressure oxygen sample (90 K compared to 160 K for the ambient sample), the NMR spectrum shows no significant shift in the two peak frequencies. However, the two peaks exhibit considerable broadening, along with structure on both the low and high frequency sides which is believed to be quadrupolar in origin. Analysis of the Ru K-edge XAFS reveals more disorder in the Ru-O bond for the high-pressure oxygen sample compared to the ambient sample. Furthermore, XANES of Ru K-edge analysis indicates no difference in the valence of Ru between the two samples. The magnetic behavior indicates the existence of some vacancies on the Ru sites for the high-pressure oxygen sample. (C) 2003 Elsevier Science B.V. All rights reserved.