Sr <sub> 2 </ Sub> Femoo <sub> 6 </ Sub> And Its Preparation And Electromagnetic Properties Of The Composite System

The double-perovskite oxide Sr₂FeMoO₆ has aroused broad interest among researchers due to its magnetoresistance effect under room temperature. This essay has prepared a series of compounds such as Sr₂FeMoO₆, Sr₂FeMoO₆/CuO, Sr₂FeMoO₆/La_0.67Sr_0.33MnO₃ and Sr₂Fe_1-xNi_xMoO₆ by sol-gel and physically mixed processes. All the samples' crystal structure, microcosmic shapes and electromagnetism peculiarities have been systemic studied through the measuring methods such as XRD, SEM, AFM, PPMS, etc. Main results of this essay are shown as follows:1) It has successfully compounded the pure poly-crystal oxide of Sr₂FeMoO₆ under different sinter temperature. The analysis of the X-ray powder diffraction and the structure analyse of it indicates that all of the samples are with a tetragonal symmetrical structure, and the space group is P4₂/m; the sinter temperature has a significant effect on the order degree of the Fe/Mo site of the samples, and the higher the sinter temperature is, the greater the order degree of the Fe/Mo site.2) The magnetic measurement of the poly-crystal Sr₂FeMoO₆ indicates that the strength of the samples' saturation magnetization has a close relationship with the sinter temperatures: the higher the sinter temperature is, the greater the strength of the samples' saturation magnetization; the electromagnetic measurement of the samples under the sinter temperature of 1373K indicates that, within the temperature zones from 10K to 300K, there is a convert from semi-conductor electric property in low temperature zones to metal electric property in high temperature zones, and furthermore, in the case that the outward magnetic field is 30000Oe, and the temperature is 10K, the magnetoresistance of the sample is up to 16.25%, and even in the low magnetic field, it is 2.8%.3) The magnetic measurement of the compound system Sr₂FeMoO₆/xCuO(x=0.1-0.5)indicates that, the strength of the samples' saturation magnetization will decrease with the increase of the compound amount of CuO; for the sample of which x equals to 0.1, the results of the electromagnetic measurement shows that, the ratio of resistance tends to increase in magnitude compared to its value before compounding, and furthermore, within the whole temperature zones from 10K to 300K, they show a semi-conductor conduction behavior; in the case that the outward magnetic field is 30000Oe, and the temperature is 10K, the magnetoresistance of the samples has increased to 33.6%, and it has also increased to 9.3% in low magnetic field; whereas, the electromagnetic measurement of the compound system Sr₂FeMoO₆/xLa_0.67Sr_0.33MnO₃(x=0.1-0.5)indicates that the strength of the samples' saturation magnetization will increase with the increase of the compound amount of La_0.67Sr_0.33MnO₃, and the ratio of resistance will increase in magnitude, with its magnetoresistance in the high magnetic field and low magnetic field up to 32% and 14.2% respectively.4) The analysis of the structures of the series of compounds of Sr₂Fe_1-xNi_xMoO₆(x=0.1-0.4) in which the digit Fe is adulterated with Ni indicates that, the adulteration of Ni causes the increase of the sequence degree of the digit Fe/Mo, and SEM shows that the doping of Ni makes the crystal grains more smaller; The magnetic measurement indicates that with the increase of the amount of Ni adulterated, the strength of the samples' saturation magnetization will increase notably. It is analyzed that it is the increase of the order degree of the B site that makes the increase of antiferromagnetic coupling between Fe³⁺ and Mo⁵⁺, which leads to the increase of the sample's saturation magnetization.