Synthesis Process And Mn Site Doping On The Magnetoelectric Properties Of GdMnO₃ Materials

GdMnO3(GMO)with orthorhombic perovskite structure is a crucial member of type II single phase multiferroic materials.It has attracted extensive attention due to the unusual physical features and remarkable magnetoelectric effect.The defects and electronic structure of the GMO materials have inherent correlation with electric and magnetic properties.However,there are no systematic researches on the effects of defect characteristics and electronic structure on the physical properties of GMO,and the inherently physical mechanism is not clear.In this paper,four experimental GMO systems were synthesized by varying the preparation method(solid-state reaction and sol-gel methods),synthesis parameter(hot isostatic temperature)and ion(Ti⁴⁺,Al³⁺)doping at Mn site.The effects of preparation method,hot isostatic temperature,Ti⁴⁺ion and Al³⁺ion doping on the microstructure and magnetic/electrical properties were investigated by positron annihilation technique,XRD,SEM et al.The correlation between the microstructure and magnetic/electrical properties of GMO systems was studied.The research content is as follows:(1)Effect of preparation methods(solid reaction and sol-gel methods)on the microstructure and magnetic/electrical properties of the GMO systems.The microstructure results show that the samples synthesized by the different methods exhibit a single-phase structure;the particle size of the sample synzhesized by the solid-state reaction method is larger;the samples prepared by both methods have cation vacancy defects,and the sample synzhesized by solid-state reaction method has higher defect concentration than that prepared by the sol-gel method.The physical property measurement results display that the samples synthesized by solid-state reaction method have better dielectric properties,while the sample prepared via the sol-gel method have a larger band gap;Mn³⁺?Mn²⁺/Mn⁴⁺can affect the magnetic transition temperature and the difference between the experimental effective magnetic moment and the calculated value.(2)Effect of hot isostatic temperature on the microstructure and magnetic/electrical properties of the GMO systems.The microstructure results exhibit that the hot isostatic pressing does not change the crystal structure,but affects the lattice parameters;the defect concentration increases,then remains constant and finally decreases with the increase of the hot isostatic temperature.Property measurement results reveal that the GMO sample prepared by hot isostatic pressing temperature at 1000°C has better dielectric properties;the hot isostatic temperature can regulate the antiferromagnetic transition temperature and the magnetization of the GMO system.The study reveals that the magnetic transition temperature and magnetization are closely related to the Mn²⁺concentration and defect concentration,respectively.(3)Effect of Ti⁴⁺ion doping at Mn site on the microstructure and magnetic/electrical properties of the GMO systems.The microstructure results display that all samples possess single phase structure while Ti⁴⁺doping causes lattice distortion;the charge compensation is mainly realized by reducing the valence state of the cation in the doping amount range of 0.00-0.10,while the decrease of oxygen vacancy concentration and the increase of Mn²⁺concentration play dominant roles when the doping amount range of 0.10-0.15;the defect concentration increases when the doping amount is 0.02,while decreases when the doping amount is higher than 0.02;Property measurement results reveal that Ti doping improves the frequency stability of the dielectric constant and reduces the dielectric loss;the magnetization decreases with the increase of Ti doping content,and it is found that defect concentration has a strong correlation with magnetization.(4)Effect of Al³⁺ion doping at Mn site on the microstructure and magnetic/electrical properties of the GMO systems.The microstructure results exhibit that all samples possess single phase structure;defect concentration firstly decreases,then increases,then decreases,and finally increases again with the increase of Al³⁺doping.Property measurement results reveal that the change tendency of the band gap is similar to that of defect concentration,and defects are closely related to the band gap;the magnetic phase transition temperature depends on the variation of the local electron density caused by Al³⁺doping,and the magnetization of the samples is mainly regulated by the dilution effect and the defect concentration.In this paper,the influence of preparation method,synthesis parameter,and ion doping on the microstructure and magnetic/electrical properties of the GMO systems was studied,and the correlation between microstructure and properties was discussed.Positron annihilation technology is innovatively introduced to study the evolution of defect characteristics and localized electron density in the GMO systems.Microdefects and local electron density were found to be the key factors affecting the physical properties of GMO systems.The research results are helpful to understand the multiferroic physical mechanism of GMO type materials,and provide theoretical and practical basis for the application of such materials in novel magnetic/electrical devices.