Preparation And Physical Properities Of Layered Perovskite Structure Sr₃Fe₂O_7-?

Fe4+ has the same electronic configuration as Mn3+(3d4),and both Fe4+-based and Mn3+-based oxides are strongly related electron systems,but they exhibit very different physical properties,especially the charge disproportionation effect in Fe4+-based oxides.We selected the Ruddlesden-Popper structure Fe4+-based oxide Sr3Fe2O7-? as the object of study.Through the material preparation and the physical properties under the magnetic field,the relationship between the magnetic field and microstructure-electromagnetic properties is established.The influence law and mechanism of the strong quantum field on the multi-quantum order and the quantum phase transition of the spin,charge and orbit of the system.The new physical phenomena and effects of Sr3Fe2O7-? and its doping system under strong magnetic field are explored and found,the innovation of this paper is that we take the electron paramagnetic resonance(ESR)as the research,so as to reveal the micro-magnetic transport of the system more profoundly.First because of the particularity of the sample in terms of preparation and preservation,including in order to getting a relatively high oxygen content,we set up a set of independent temperature control of the ultra-high critical autoclave equipment for the preparation of samples to provide a variety of regulation.The preparation of single crystal is mainly based on the optical floating zone method,and this method is briefly introduced.The working principle of electronic paramagnetic resonance(ESR)is also introduced.Then we studied the Sr3Fe2O6.6 single crystal samples with oxygen vacancy.The oxygen content of the sample was obtained by XPS test.The experimental results show that the lattice structure of Sr3Fe2O6.6 is tetragonal structure,compared to Sr3Fe2O7,there is no phase change due to the decrease of oxygen content,but the Neel temperature TN drops from 120 K to 62 K.Zero field cooled(ZFC)and field-cooled(FC)bifurcation behavior in terms of magnetic properties,this is due to low temperature ferromagnetic and antiferromagnetic competition caused by each other.The M-H curve of the sample has a small hysteresis loop to prove this well.And the relationship between the reciprocal 1/? of the magnetic susceptibility and the temperature is deviated from the linear behavior.The ESR measurement shows that this is due to the generation of local magnetic moments.Through the resistivity measurement,at low temperatures the resistivity behavior is well fitted by the three-dimensional Mott variable range jump model.The heat transport is well matched to the Thirring model in the measured full temperature range.Furthermore,we systematically studied the doping effect of the layered Sr3Fe2O7-? compound Nb-doped series of polycrystalline samples.The experimental results show that the relationship between the reciprocal of the magnetic susceptibility and the temperature has a deviation from the linear behavior.The antiferromagnetic transition temperature TN decreases monotonically with the increase of doping amount.As the doping amount increases,the resistivity increases monotonically,at low temperatures,it is well suited to the three-dimensional variable range jump model.The antiferromagnetic transition temperature TN of the sample treated by oxygen pressure was significantly increased and the resistivity was decreased.Finally,we have made some prospects for the study of Sr3Fe2O7-? system.The most surprising physical properties in the system are the phenomenon of charge disproportionation,which can be doped by the 4d,5d element,and the combination of the Mossbauer spectrum may reveal the nature of charge disproportionation.And we also believe that the relative lack of Sr3Fe2O7-? system and its doping system through ESR,if you strengthen the application of the means,may find and reveal more novelty.