Modulation Of Pulsed High Magnetic Field And Doping On Magnetic And Electric Properties Of (Sm,Bi) FeO₃

ABO₃ type iron oxides,which possess such physical properties as ferroelectricity,piezoelectricity,ferromagnetism and antiferromagnetism due to their complex interactions of spin,orbit and charge,have potential applications in electronic information technology,memory devices and aerospace etc.Due to BiFe O₃ and SmFe O₃ possess extremely high Neel temperature,they are antiferromagnets at room temperature,which make it possible to achieve room temperature multiferroic behavior.In this dissertation,the properties of BiFe O₃ and SmFe O₃,including to the magnetism,polarization,dielectricity,optical property,structure and other aspects,as well as the modulation mechanism of high magnetic field and doping on its properties,are investigated.1.The role of high magnetic field in scientific research was briefly introduced,and the structure and properties of ABO₃ type oxides were simply summarized.The structure,magnetism,polarization,neutron diffraction,magnetostriction and other aspects of BiFe O₃were introduced.The research status of SmFe O₃ in structure,magnetism and pyroelectricity were introduced,the influence of ion doping are also introduced.2.The strong coupling between spin,charge and lattice of BiFe O₃ single crystal was studied.It is found that under the action of pulsed high magnetic field,the spin cycloid phase transfers into a canted antiferromagnetic phase,and the spontaneous polarization is weakened,and the magnetostrictive effect is produced.The critical fields of magnetic phase transitions are moved to lower magnetic field region by the applied electric field,which indicates that there are complex coupling among magnetization,polarization and lattice.The strong anisotropic magnetoelectric coupling behavior of BiFe O₃ single crystal was observed,and the magnetoelectric coupling model of BiFe O₃ single crystal was established.The study on synergetic response of ordering parameters such as spin,charge and lattice in the magnetic phase transition of BiFe O₃ single crystal,is beneficial to the exploration of spintronic devices and novel multiferroic materials with strong ME coupling.3.SmFe O₃ and SmFe_0.9Mn_0.1O₃ single crystals were grown by optical floating zone method.Their magnetic properties were studied by steady state magnetic field and pulsed high magnetic field.In particular,the effects of magnetic field and doping on spin switch transition,the spin reorientation,the destruction of antiferromagnetic coupling and other behaviors were comprehensively studied.The relationship between the dielectric behavior and the strain induced by temperature in SmFe O₃ and SmFe_0.9Mn_0.1O₃ single crystals was studied.The experiments provide a clear physical picture of the magnetization behavior of SmFe O₃ sinele crystal under high pulsed magnetic field,and provide an effective means to study the dominated effects between rare earth ions and transition metal ions on the complicated magnetization behavior of ABO₃oxides.Doping Mn has an obvious effect on magnetic anisotropy,strain,spin reorientation and magnetization behavior of SmFe O₃:Mn-dopant reducing the net moment of Fe³⁺/Mn³⁺sublattice,which results in the compensation temperature shifted to higher temperature region;The pinning effect of Mn-dopant leads to the spin switching transition becomes difficult;The J-T Mn³⁺-ion induced local distortion change the anisotropic field of SmFe O₃,which causes that the spin reorientation transition becomes easy;Doped Mn³⁺enhances AFM coupling between Sm³⁺and Fe³⁺/Mn³⁺sublattices,which enhances the critical fields of the AFM coupling breaking;Mn-dopant inhibits the competition between Sm³⁺and Fe³⁺sublattices during the destruction of AFM coupling,which eliminates multi-step magnetic phase transition;Mn-dopant eliminates the temperature induced reversal of strain direction,which results in the absence of dielectric peak.