Synthesis And Properties Of Magnetoresistance Materials Sr_2-xRe_xFeMoO₆by Microwave Sintering

In this paper, the magnetoresistance materials Sr₂FeMoO₆with double perovskitestructure and series of A site doped compounds Sr_2-xGd_xFeMo₆and Sr2-xLaxFeMoO6（x=0,0.1,0.2,0.3）were synthesized by microwave sintering method. X-ray powder diffraction（XRD）, Fourier transform infrared spectroscopy （FT-IR）, vibrating sample magnetometer（VSM） and four-point probe method were used to analyze and characterize the phase structure,magnetic and electric properties of the samples. Meanwhile, the degradation activity ofSr₂FeMoO₆for dye Acid Black10B and Acid Red B solutions were investigated.Fisrt, the influence of microwave absorbent species and reduction time on the phasestructure, magnetic and electrical transport properties of samples were investigated. MnO2isconfirmed as the better microwave absorber and the optium reduction time is30min. Theas-synthesized sample is Sr₂FeMoO₆with tetragonal crystal structure and I4/mmm spacegroup. The unit cell parameters are a=0.5587nm, c=0.7894nm, volume=0.2464nm3, andthe calculated grain size is31.62nm. The sample Sr₂FeMoO₆is ferromagnetic with themagnetic transition temperature of about380K. Under1.0T magnetic field, the saturationand spontaneous magnetization is16.528A·m2/kg and13.21A·m2/kg at room temperature.The magnetoresistance ratio of the sample is28.02%. The sample exhibits typicalsemiconductor behavior. The conductive mechanism of Sr₂FeMoO₆is highly depended ontemperature: within the temperature range of100³00K, the mechanism is attributed to thesmall polaron variable-range hopping model; while it is ascribed to the adiabatic smallpolaron model within the temperature range of80¹00K.Then, the influence of partial replacement of Sr2+in Sr₂FeMoO₆with middle-heavy rareearth ions Gd³⁺or light rare earth ions La3+on the phase structure, magnetic and electricaltransport properties of samples were investigated. The results show that all the samplesSr_2-xGd_xFeMo₆and Sr2-xLaxFeMoO6（x=0,0.1,0.2,0.3） are tetragonal crystal structure withI4/mmm space group. With the increase of doped Gd³⁺, cell volume increases firstly and thendecreases, accompanied by a small amount of impurity phase Gd2O3. But, the doping of La3+makes the cell volume decrease. Magnetism testing results show that the samplesSr2-xGdxFeMoO6and Sr2-xLaxFeMoO6are ferromagnetic, and the magnetic transitiontemperature is above room temperature. The saturation magnetization decreases with thedoping of Gd³⁺, but magnetoresistance can be improved significantly to61.66%when the doping content of Gd³⁺x=0.3. The doping of La3+also make the saturation magnetizationdecrease, but magnetoresistance can be increased to36.80%when the doping content of La3+x=0.1. All the samples exhibit typical semiconductor behavior.Last, the degradation activity of Sr₂FeMoO₆for dye solutions was investigated. Theresults show that the sample Sr₂FeMoO₆shows excellent degradation activity for dye AcidBlack10B and dye Acid Red B. When the initial concentration of Acid Black10B is20mg/Land the dosage of Sr₂FeMoO₆is60mg/50mL, the decolorizing rate can reach to98%within20min under ultraviolet lamp, daylight lamp or sunlight irradiation, and about97%within50min in dark condition. When the initial concentration of Acid Red B is20mg/L and thedosage of Sr₂FeMoO₆is100mg/50mL, the decolorization rate is close to100%within30min under light irradiation or60min with no light.