Enhancing Magnetic and Magnetotransport Properties by Topotactic Reduction of the Sr2Fe1.33Mo0.66O6 Double Perovskite

CARLOS ALBERTO LÓPEZ; MARÍA DEL CARMEN VIOLA; JOSÉ CARMELO PEDREGOSA; JOSÉ ANTONIO ALONSO; MARÍA TERESA FERNÁNDEZ-DÍAZ

EUROPEAN JOURNAL OF INORGANIC CHEMISTRY

WILEY-V C H VERLAG GMBH

Lugar: Weinheim; Año: 2010 vol. 2010 p. 4110 - 4120

1434-1948

Sr2Fe1.33Mo0.66O6 (alternately written as Sr3Fe2MoO9) perovskite has been prepared in polycrystalline form by thermal treatment, in air, of previously decomposed citrate precursors. This material has been studied by X-ray and neutron powder diffraction (XRPD and NPD), magnetic and transport measurements. At room temperature, the crystal structure is cubic with a = 7.8585(2) Å and V = 485.30(2) Å3, defined in the space group Fm-3m. Magnetic measurements indicate a ferromagnetic ordering below TC = 246 K. As prepared, the sample is an electrical insulator. A topotactic reduction of the stoichiometric sample performed at 600, 700, and 800 °C, in H2/N2 flows, leads to the oxygen-deficient double perovskites, Sr2Fe1.33Mo0.66O6?δ with increasing δ values. The evolution of the crystal structure upon reduction has been studied from XRPD and NPD data. For the sample obtained at 800 °C, exhibiting the largest δ value, the low-temperature evolution from NPD data was investigated between 2 K and 500 K: in all the temperature range the crystal structure is cubic with space group Fmequation imagem; at room temperature a = 7.87060(6) Å and V = 487.555(6) Å3. The magnetic behavior of this reduced sample suggests the presence of ferromagnetic domains characterized by Curie temperatures with TC > 400 K. The conductivity dramatically increases upon H2 reduction. Moreover, this reduced sample exhibits magnetoresistance, as high as 2.5 % at room temp. for H = 5 T. Magnetic and magnetotransport results are consistent with a large component of itinerancy for down-spin Mo t2g electrons, injected through hydrogen reduction.