| Multiferroic materials are a term coined by Schmid for crystals "two or three of the basic properties occur simultaneously in the same phase, the basic properties are ferroelectricity, ferromagnetism and ferroelasticity". Multiferroic materials display the good performances of ferroelectricity, ferromagnetism (antiferromagnetism) and ferroelectricity (anti ferroelectricity). However, the strong coupling between the different kinds of properties, which makes multiferroics possess of new potential properties that is different from the basic properties mentioned above. So, multiferroic materials become a time honored research subject in materials subject.With the development of the technological, the miniaturization and diversification of electronic devices, it is both scientifically interesting and technologically challenging to combine the function of multiferroic materials and finite-size effect of nanoparticles to further meet the needs of development of science, which makes the multiferroic nano-materials become the hotresearch subject. However, there are very few materials that can exhibit both magnetization and electric polarization at room temperature, which hides the interest of the multiferroic. GaFeO3exhibits the piezoelectric property, but its magnetic translated temperature is lower than the room temperature. So the way of improving the magnetic translated temperature is extensively studied. There have been a lot of results showed the following routes, such as the optimization of the preparation process of the materials, methods, theoretical simulation and doping other ions. These studies can conduct a comprehensive evaluation and research. We conclude that the low-temperature of annealing conditions more likely to improve the material’s magnetic phase transition temperature. Together with the earlier studies in this thesis, we prepared by the single-phase GaFeO3materials using the sol-gel method, and selected transition metal ions replace the ions on the Fe or Ga sites. The crystal structure, magnetic, the magnetic transited temperature and dielectric properties of the prepared samples were investigated. The main conclusions are main as follows:1. Co2+ions doped GaFeO3, GaFe1-xCoxO3(GFCOX)(x=0.00,0.01,0.02,0.03,0.04,0.05), were prepared using a sol-gel method. The crystal structure, magnetic and dielectric properties of the prepared samples were investigated. It was found that the substitution of Co2+ions for Fe3+ions could increase Curie temperature of GFCOx. The other magnetic properties (M at10kOe=1.80emu/g, HC=80Oe and Mr=0.13emu/g) of GFCOx were also enhanced by the doping of Co2+ions, and were increased with the content of the Co2+ions doping. The dielectric properties of GFCOx could be effectively improved in the range of the tested frequency, via the doping with a suitable amount of Co2+ions.2.Ga2-xFexO3(GFOx)(x=1.05,1.10,1.15,1.20), were successfully prepared using a sol-gel method. The crystal structure, magnetic and dielectric properties of the prepared samples were investigated. The gain size of all the samples rangs from48nm to52nm. It was observed that the magnetization (M=7.00emu/g) at10kOe, remnant magnetization (Mr=2.9emu/g) coercivities (HC265Oe) and Curie temperature (TC=340K) of GFOx nanoparticles visibly increase with x value. The sample of x=1.20displayed excellent magnetic properties at room temperature. Moreover, the dielectric properties of polycrystalline GFCOx could be effectively improved through changing x value, but does not follow the law displayed in the single crystal materials.3.(1-x) GaFeO3-x NiGaFeO4(x=0.00,0.05,0.10,0.15) composite multiferroic materials were prepared by sol-gel method. Their magnetic properties, dielectric properties and the magnetic capacitor were investigated and studied. The results showed that the samples not only existed the magnetic and dielectric properties but also observed the magnetic capacitor in a certain magnetic field. We also found the magnetic capacitor was closely related to the magnitude of applied magnetic field and the electric field of frequency, as well as the composition ratio of the two-phase materials (x). |
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