Study On Magnetoelectric Properties Of Sr₂FeMoO₆ Doped With Fe/Mo Sites

Double perovskite oxide is a very important member of perovskite oxides.Because of its rich physical connotation,it has received extensive attention from scientific researchers in recent years.In 1998,Kobayashi et al.discovered that the double perovskite oxide Sr₂FeMo O₆（SFMO）and triggered the subsequent research boom.Based on the density functional theory,they found that SFMO will have 100%spin polarization near the Fermi level through calculation of the band structure,indicating that it will have a great use in spintronic devices.SFMO has a magnetic phase transition point near room temperature,semiconductor characteristics and low field magnetoresistance.In this paper,SFMO is mainly used as the research object to discuss the influence of Mo vacancy,Fedoping and solution PH on the structure and performance of the material.Specifically include the following three aspects:（1）Sr₂FeMo_（1-x）O₆（x=0.00、0.01、0.03 and 0.04）samples were prepared by sol-gel method,and the influence of Mo vacancies on its structure,magnetic properties and transport properties was studied.Through XRD test analysis,it is found that all samples are single-phase and belong to the I4/m space group.From the scanning electron microscope image,the particle size analysis software calculates that the average particle size of the samples with x=0.00、0.01、0.03 and 0.04 are 1.26μm、1.32μm、1.27μm and 1.19μm,respectively.The relationship between resistivity and temperature was measured by the comprehensive physical property measurement system（PPMS）.From the figure,it can be seen that all samples exhibit semiconductor behavior.The field cooling curve and isothermal magnetization curve show the transition of the sample from the ferromagnetic state to the paramagnetic state.Under a 2.5 T magnetic field,the magnetic entropy changes of the samples are 0.53,0.6,0.58 and 0.57 Jkg^-1K^-1,respectively.（2）The double perovskite Sr₂Fe_（1+x）Mo（1-x）O₆（x=0.00、0.01、0.03）was prepared by the sol-gel method,and the effect of Feion doping on its structure,transport and magnetic properties was studied.X-ray diffraction results show that the obtained samples are pure phases,and the order of Fe/Mo is 11.07%,10.78%and 10.47%,respectively.By observing the micro morphology of the sample and calculating the particle size analysis software,the average particle size of the sample is 0.77μm、1.00μm and 0.87μm,respectively.Under 5 K,the saturation magnetic moments of all samples are 3.16、2.69 and 2.71μ_B/f.u,and the coercive fields are 63.94、71.85 and 94.41 Oe,respectively.The results show that Feion doping reduces the saturation magnetic moment and increases the coercive field.Under an external magnetic field of-9T～9 T,the MR-H curves at low temperature 5 K and room temperature 300 K were tested respectively,and it was found that the magnetoresistance value at low temperature was relatively large,but as the Feion doping amount increased,the magnetoresistance would be suppressed.（3）In the process of sol-gel synthesis of double perovskite Sr₂FeMoO₆,the influence of the p H value（PH=3,6,10）of the sol system on the magnetoelectric properties of double perovskite SFMO was explored.The scanning electron microscope image shows that the sample with a PH value of 6 has higher crystallinity,and the average particle size value is also the largest,which is 0.85μm.At a low temperature of 5 K,the saturation magnetic moment values of the three samples are 3.16,2.79,and 3.44μ_B/f.u,respectively.In order to study the electrical transport performance of the sample,theρ-T diagram of the change trend of resistivity with temperature（5-300 K）under different magnetic fields（0 T,5 T,9 T）was tested.The sample with PH=6 shows semiconductivity under zero magnetic field or under the applied magnetic field;while the two samples with PH=3 and 10 show semiconductivity under zero magnetic field,after 5 T and 9 T magnetic fields are applied,they show metallicity.Under 5 K,the magnetoresistance value of the sample with PH=3 reaches 80%at 9 T.