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 99,101 Ru zero-field spin-echo NMR, and Ru K-edge XAFS, 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 MHz and 72.2 MHz corresponding to the 99Ru and 101Ru 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.Comment: Proceedings of the 3rd Polish-US Workshop on Magnetism and Superconductivity of Advanced Materials, July 14-19, 2002, Ladek Zdroj (Poland), to appear in Physica

Synchrotron radiation studies of local structure and bonding in transition metal aluminides and rare earth transition metal magnetic nitrides. Final report, August 1, 1990--July 14, 1993

The following areas of study are reported on: bonding and near neighbor force constants in NiAl, CoAl, FeAl via temperature dependent EXAFS; alloys formed when Fe or Ga is microalloyed into a NiAl matrix; EXAFS studies of nitrided versus non nitrided Y{sub 2}Fe{sub 17}; and transition metal x-ray spectra as related to magnetic moments

Studies on the Local Structure of Dilute 3d Transition Metal Ternary Dopants in L12 Ordered Ni3Al-Based Alloys

We have utilized the technique of XAFS to study the local environment of transition metal (TM) ternary dopants (Ti, V, Cr, Mn, Fe and Co) in Ni75TMxAl25-x. In γ-Ni3Al, the first shell around Al consists of 12 Ni atoms. Ni is surrounded by 8 Ni and 4 Al atoms. In all cases, the dopant K-edge XAFS results show only Ni backscattering contribution in the first peak of the Fourier transform. Al backscattering contribution is either completely absent or is so weak that it is masked by the strong dopant-Ni bond. The number of Ni near neighbors suggests that for Ti, V, Cr, Mn and Fe absorbers, a majority of the dopant atoms occupy the Al sublattice. However, even in the case of Co dopants where studies by others indicate that the Co atoms occupy the Ni sublattice, no Al backscattering contribution can be detected. Also, the XANES of the various dopants exhibit a special feature at the edge, which appears to be due to p-d mixing

KRYPTON XANES STUDIES IN IMPLANTED SYSTEMS

On a mesure la dépendance en température de l'absorption des rayons X près du seuil K (XANES) pour le krypton implante dans du niobium, de l'aluminum et du grafoil. Pour les cibles d'aluminum et de grafoil on observe une augmentation des "white line" mesurées avec des basses températures. Après les mesures avec XANES, nos échantillons on été études par RBS.Temperature dependent K edge XANES of krypton have been measured for krypton implanted into niobium, aluminum and grafoil. For the cases of aluminum and grafoil targets, there is a marked enhancement of the observed white line for the XANES measured at lower temperatures. In addition to the XANES studies, our samples are further characterized by Rutherford backscattering spectroscopy

DIFFERENCE IN Fe ATOM ENVIRONMENTS BETWEEN CuFe (2% Fe) AND CuAuFe (1 AND 3% Fe) ALLOYS

According to recent 57Fe-Mössbauer measurements made at 4.2K, Fe atoms in Cu69Au30Fe1 and Cu67Au30Fe3 are dominantly ( > 80%) ferromagnetic, whereas Fe atoms in Cu98Fe2 manifest antiferromagnetic interactions (< 10% ferromagnetic). The Fe K-edge XANES and EXAFS measurements have been made on these alloys. Fluorescence, as well as transmission, data have been obtained. The XANES and EXAFS spectra for the CuAuFe alloys are quite similar to the spectra for α-Fe, which seems to reflect the clustering of ferromagnetic bcc Fe. On the other hand, the XANES and EXAFS for Cu98Fe2 closely resemble those of fcc Ni, strongly indicating the environment of antiferromagnetic fcc [MATH]-Fe. Moreover, the Fourier transform for Cu98Fe2 shows more smeared out higher shell peaks compared with those for CuAuFe. This may be the result of varying sizes of Fe clusters

NMR study of the atomic structure for heat treated metglas 2605 CO

Spin-echo NMR measurements of the 11B, 57Fe and 59Co internal hyperfine field distributions in both as-fabricated and heat treated Metglas 2605 CO are presented. These spectra provide a clear picture of the evolution of various phases with annealing