NMR study of (Sr,Ba,La)2Fe1+xMo1-xO6 double perovskites

Dariusz A. Zajac 2Czesław Kapusta 2Peter C. Riedi 3Marcin Sikora 2Colin J. Oates 2Damian Rybicki 2Jose M. De Teresa 1Clara Marquina 1Ricardo M. Ibarra 1

1. Universidad de Zaragoza-CSIC, Facultad de Ciencias, Pedro Cerbuna 12, Zaragoza 50009, Spain
2. AGH University of Science and Technology (AGH), al. Mickiewicza 30, Kraków 30-059, Poland
3. University of St. Andrews, School of Physics and Astronomy, St. Andrews KY16 9SS, United Kingdom

Abstract

The 95Mo and 97Mo nuclear magnetic resonance study of (Sr,Ba,La)2(FeMo)O6 double perovskites is reported. The compounds exhibit a significant low field magnetoresistance at room temperature. Compounds with different (SrBa) - La composition, different content of cation vacancies as well as different Fe - Mo ratio have been studied. The frequency swept spin-echo spectra have been measured at 4.2K and no applied magnetic field. The parent compound, Ba1.6Sr0.4FeMoO6, shows a main line at 59 MHz and a satellite line at 43 MHz. They are attributed to the ideal and defect (antisite neighbours and antiphase boundaries) sites of molybdenum. Both lines correspond to 95Mo and 97Mo resonances, which are unresolved due to very close gyromagnetic ratios. The spectrum of the 10% La doped sample, Ba1.44Sr0.36La0.2FeMoO6 shows a higher intensity of the low frequency satellite line, which indicates an increased number of defect sites. The main line is at higher frequencies compared to the parent compound and shows a satellite structure at the high frequency side. An increase of the number of vacancies at the same La doping Ba1.28Sr0.32La0.2FeMoO6 further increases the population of defect sites. In the Ba1.28Sr0.32La0.2Fe1.2Mo0.8O6 compound the change of the Fe-Mo stechiometry significantly decreases the amount of antisite defects. The results are analysed in terms of the influence of doping on the Mo magnetic moments and population of defect sites. A relation to the magnetic and transport properties of the compounds is discussed.

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Presentation: oral at E-MRS Fall Meeting 2003, Symposium D, by Dariusz A. Zajac
See On-line Journal of E-MRS Fall Meeting 2003

Submitted: 2003-05-27 17:53
Revised:   2009-06-08 12:55
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