Y.C. Hu 1 , X.S. Wu 1 , J.J. Ge 1 , G.F. Cheng 2

1. 2009 IEEE Summer School Gd doping effects on structure and magnetic property in Sr2FeMoO6 ABSTRACT The crystal structure and magnetic property for the double perovskite oxides Sr2-xGdxFeMoO6 (0≤x≤0.25) have been investigated. X-ray diffraction results show that all samples crystallize in single phase, with the tetragonal symmetry. The unit cell parameters of a, c and the unit cell volume of v are gradually decreasing with x increasing, which can be interpreted by smaller Gd3+ substitution of Sr2+. The a/c, and the tolerance factor t are monotonously decreasing against doping content x suggests that smaller Gd3+ substitution of Sr2+ leads to reduction of symmetry lattice. The temperature dependence of magnetization suggests that paramagnetic–ferromagnetic transition widens with increasing x. The experimental effective magnetization is not consistent with the calculated value suggests that Gd moment may aligns anti-parallel to the Fe moment. The Curie temperature of the compounds is decreased pronouncedly and the order concentration is the main reason for Tc. MOTIVATION In order to extend the working range of the materials for the potential applications, many efforts have been devoted to the understanding of magnetic oxides. Electron-doping has been extensively studied recently and make a great progress. Ion Gd+3 is the most magnetic ion among the lanthanide ions . In order to understand in detail the electron doping and magnetic ion effect on structure and magnetic property of the double perovskites, we synthesized the compounds . EXPERIMENTAL Samples of Sr2-xGdxFeMoO6 are prepared by standard solid-state reaction. Stoichiometric powders of SrCO3, Fe2O3, MoO3 and Gd2O3 are mixed, ground and heated at 900 ℃ for 10 h in air. The pre-reacted mixture is then finely ground, pressed into pellets and sintered at 1280 ℃ in a stream of 5% H2/Ar gas for 15 h with several intermediate grindings. Structure of the sample is examined by X-Ray Powder Diffraction (XRD) . The XRD data is analyzed by means of the Rietveld refinement program GSAS . Temperature dependence of magnetization curves were recorded by a vibrating sample magnetometer in a field of 500 Oe. RESULTS AND DISCUSSIONS Fig.1. shows the representative patterns for Sr2-xGdxFeMoO6. The vertical bars at the bottom indicate the Bragg reflection positions. The lowest curve is the difference between the observed and the calculated XRD patterns. Inset shows that the ordering concentrationηdepends on doping content x. X-ray diffraction results show that The unit cell parameters of a, c and the unit cell volume of v are gradually decreasing with x increasing, which can be interpreted by smaller Gd3+ substitution of Sr2+. Fig.5 shows the effective magnetization dependence of doping content x. Filled square is the experimental value, Filled circle is theoretical value from . The difference between the theoretical and the experimental value widens with increasing x. Gd3+ is the most magnetic ion among the lanthanide ions .The difference is mainly due to that the formula does not consider the Gd3+ moment. The Gd3+ moment aligns anti-parallel to the Fe moment makes Me smaller. Fig.3 shows the unit cell of SFMO, The Rietveld refinement results suggest that Gd3+ effectively occupy at Sr2+ site .the distortion in FeO6 octahedron is reduced and that in MoO6 octahedron is augmented . Fig. 4 shows magnetization of the compounds dependence of temperature. The paramagnetic–ferromagnetic (PM–FM) transition widens with increasing x. There are anti-ferromagnetic Fe–O–Fe patches within the ferromagnetic matrix due to AS defect. The AS defect increase with the increasing Gd3+ doping and the size of these patches become larger. Magnetic moment at Mo-site is another important reason. The magnetic moment at Mo-site increases due to doping electrons injection into Mo orbit. The overall ferromagnetic interaction weaken due to Mo moment aligns anti-parallel to the Fe moment. Y.C. Hu1, X.S. Wu1 , J.J. Ge1 , G.F. Cheng2 1. Nanjing National Laboratory of Microstructures, Department of Physics, Nanjing University, Nanjing 210093, China 2. Shanghai Institute of Ceramics, Chinese Academy of Sciences, 1295 Dingxi Road, Shanghai 200050, China Fig.2 shows a/c (left) and t (right) against doping content x. The solid lines are linear fit of the a/c and t respectively. The Fig. suggests that smaller Gd3+ substitution of Sr2+ leads to reduction of symmetry lattice. Fig.6 shows Dependence of the Curie temperature on doping content x. The inset shows the relation between TC and the order concentration. The inset clearly presents that the order concentration is the main reason for Tc. CONCLUSIONS The crystal structure of Sr2-xGdxFeMoO6 and magnetic properties of the series have been investigated. The powder X-ray diffraction results show that all samples crystallize in single phase. Rietveld refinement suggests that the crystal structure of all samples is tetragonal. a, c, and v are gradually decreasing, which can be interpreted by smaller Gd3+ substitution of Sr2+. The a/c and the tolerance factor t are monotonously decreasing against increasing doping content x suggests that smaller Gd3+ substitution of Sr2+ leads to reduction of symmetry lattice. The temperature dependence of magnetization suggests that paramagnetic–ferromagnetic transition widens with increasing x. The Curie temperature of the compounds is decreased pronouncedly and the order concentration is the main reason for Tc. ACKNOWLEDGEMENT This work is supported by NNSFC (10974081, 10774065, 10523001) and NKPBRC(2006CB921802, 2009CB929500).