Practical applications of colossal magnetoresistive(CMR) oxides are limited by the large magnetic fields and/or low temperature required to observe a significant change in electric resistivity[1-5]. In recent years，research on tunneling mag... Practical applications of colossal magnetoresistive(CMR) oxides are limited by the large magnetic fields and/or low temperature required to observe a significant change in electric resistivity[1-5]. In recent years，research on tunneling magnetoresistance(TMR) is a very active field because of its scientific interest and potential technological applications[6].Polycrystalline Sr2FeMoO6 perovskite is a candidate for magnetic sensors owing to its high ferromagnetic transition temperature …（Tc~420K）and the half-metallic electronic band structure predicted theoretically [7]. The conduction electrons in this compound are expected to be highly spin-polarized even at room temperature. More recently， perovskite Sr2FeMoO6 with nanometer grain size showed large magnetoresistance(~20%) at a low magnetic field of 4k Oe and at room temperature[8].Dai et al.[9]observed two different ordered structures in polycrystalline Sr2FeMoO6 perovskite: the double perovskite and the superstructure with tripled c-axis(ST).In this paper， another new layered structure of body-centered tetragonal phase (BT) is reported for the polycrystalline magnetoresistive Sr2FeMoO6 sample.
Ceramic samples of Sr2FeMoO6 were prepared by standard solid state reaction. Stoichiometric materials of SrCO3，F(xiàn)e2O3 and MoO3 were mechanically mixed， and then calcined at 950℃ for 4h in air.The calcined mixture was then ball-milled and made into pellets followed by sintering at 1250℃for 4h in carbon monoxide atmosphere.Transmission electron microscopy(TEM) specimens were prepared by mechanical polishing，dimpling and ion milling.Electron diffraction patterns were taken at 120kV using a Phillips CM12 electron microscope， and high resolution TEM imaging was conducted using JEOL 2010 microscope. Energy dispersion of X-rays(EDX) was conducted by TEM attached with EDAX PV9100. 展開
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