Study On The Magnetic And Dielectric Properties Of Ion-doped CuFeO₂ Multiferroics Materials

Delafossite oxides CuFeO₂ material is one of the research focuses in the field of multiferroics materials due to its unique magnetic structure and strong magnetoelectric coupling effect.However,the ferroelectric property of CuFeO₂is weak and the physical mechanism of magnetoelectric coupling is still unclear.Therefore,various attempts should be adopted to further explore the structure and properties of CuFeO₂.In this paper,several ions doped CuFeO₂ ceramic samples are prepared by solid statereaction method,and X-ray photoelectron spectroscopy,Raman spectroscopy,Positron Annihilation spectrum and other technologies are carried out to study the influence of ion occupation and features on the microstructure and defects of CuFeO₂ materials,and the correlation between the microstructure,magnetic properties,electrical properties,optical properties of CuFeO₂ system is further investigated.Therefore,the research resultshave certain value to the theoretical research and practical application of CuFeO₂ based ceramics.In this paper,four CuFeO₂ system samples with Fe sites doped by Zr⁴⁺,Mn⁴⁺and Cu sites doped by Li⁺,Ca²⁺/Sr²⁺/Ba²⁺are synthesized.The effects of doping ion concentration,size,valence state,magnetic properties and occupied positionon the microstructure of CuFeO₂ system are systematically studied,and the internal correlation between the microstructure and physical properties is explored.The main conclusions are as follows:1.Effects of non-magnetic transition metals Zr⁴⁺ion doping at Fe sites on the microstructure and magnetic properties of CuFeO₂.The results show that the grain growth is inhibited,and the vibration and polarization strength of the?Fe,Zr?-O bond are changed by Zr⁴⁺doping;Zr⁴⁺doping reduces the defects size and increases the defects concentration of CuFeO₂system.The stability of the antiferromagnetic phase in the CuFeO₂ system at low temperature is destroyed and the magnetic transition temperature is shifted to the low temperature region by Zr doping.It is considered that lattice distortion,defect evolution and second phase induced by Zr⁴⁺ion dopingwill affect the magnetic behaviors of CuFeO₂ system.2.Effect of magnetic transition metal Mn⁴⁺ion doping at Fe sites on the microstructure and magnetic properties of CuFeO₂.The results show that Mn⁴⁺ion with low concentration?x?0.05?can effectively enter into the CuFeO₂ lattice and promotes grain growth;the valence stability of Fe³⁺and Mn⁴⁺is destroyed by Mn⁴⁺doping,and the system coexists with Fe³⁺/Fe²⁺and Mn⁴⁺/Mn³⁺ions.Antiferromagnetic transition temperature T_N2 is not observed in the x?0.05samples,the formation of the four-sublattice antiferromagnetic phase?4SL?in the system is inhibited by Mn⁴⁺doping at low temperature.It is considered that the changes ofgrain size,and charge compensation effects induced by Mn⁴⁺ion dopingplay an important role in the magnetic properties of CuFeO₂ system.3.Effect of alkali metal Li⁺doping at Cu site on microstructure and physical properties of CuFeO₂.The results show that the grain growth is inhibited by Li doping;the vacancy defect characteristics of the system and the local electron density of CuFeO₂ are observably affected by Li doping.All the samples exhibit giant dielectrics?>10⁴?and low loss value,and the dielectric properties of the CuFeO₂ system are affected by Li doping;the optical band gap value of the CuFeO₂ system is reduced by Li doping;The stability of the antiferromagnetic phase in the system is not affected,but the magnetic properties of the system is improved by Li doping.It is considered that the changes of lattice distortion and vacancy defects caused by Li doping can inhibit the spiral spin modulation structure,thus affects the magnetic properties of the system.4.Doping of different alkaline earth ions with different radius(A²⁺=Ca²⁺,Sr²⁺,Ba²⁺)at Cu site on microstructure and physical properties of CuFeO₂.The results show that alkaline earth ions with larger radius doping causes lattice distortion,destroys the stability of the valence state of Fe³⁺ions,and induces the coexistence of Fe³⁺/Fe²⁺;the doping of A²⁺reduces the density of samples and promotes the grain growth.Ba doped CuFeO₂ samples display the maximum density?5.376 g/cm³?;the doping of alkaline earth ions with larger radius causes the changes of vacancy defect size,concentration and the chemical environment around thepositron annihilation points;A²⁺doping destroys the stability of the antiferromagnetic phase at low temperature and the magnetic transition temperature shifts to the lower temperature region.It is considered that A²⁺ions doping at Cu site changes the cation vacancy concentration,internal electron structure and the magnetic structure of the system,and thus affects the magnetic properties of the system.In this paper,ions doping at Fe sites and Cu sites in CuFeO₂ samples are synthesized,the effects of doping ion featureson the crystal structure,micromorphology,electronic structure,defect characteristics and other microstructures of CuFeO₂ system are studied and compared.The results of microstructure changes on the magnetic,electrical and optical properties of the system induced by ion doping provide experimental data for the research of physicalmechanism and application of multiferroic CuFeO₂ system.In particular,this paper innovatively introduces positron annihilation technology to explore the defect evolution characteristics of CuFeO₂ system,and studied the correlation between defect characteristics and physical properties.The research results provide experimental data andresearch foundation for the application of CuFeO₂ materials in the fields of optical,electrical,and magnetoelectric coupling devices.