Investigations On The Preparation, Structrure Transition And Magnetic Property Of Multiferroic Material Ga_2-xFe_xO₃ Ceramics

Multiferroic materials, that show ferroelectric order, (anti)ferromagnetic and/or ferroelastic order in the same phase and a coupling between them over a certain range of temperature, are extensively studied because of the potential application to provide a wide range of applications, including the field of spintronics, sensors, data-storage media, etc. Amonge these materials, the ferrimagnetic GaFeO₃ with higher Curie temperature (Tc=200K) has attracted much attaintion in recent years.In this thesis, a series ofε-Ga_2-xFe_xO₃ (0.8≤x≤1.3) samples have been successfully prepared by solid state reaction. The occupations of Fe ions at four different cation sites are determined by Rietveld refinement, and their effects on high-field magnetization M and Curie temperature Tc have been investigated. The results shows that the lattice parameters of a, b, and c monotonously rise with increasing Fe content. The values of Tc and M are consistent with those of single crystal, which can be calculated by a simple statistical model using experimental value of Fe content at four different cation sites. The calculated Tc and M are well fitted to experimental results. The non-effect Fe ions exist in the crystal due to the disordered distribution, which have no contribution to ferrimagnetism and show different magnetic behavior. Their presence in the ferrimagnetic ordering background gives rise to the observed frequency suppression of the peak height in the ac susceptibility, demonstrating the frustration effect.According to the previous reports, the Fe ions distribution and magnetic property ofε-Ga_2-xFe_xO₃ compounds are dependent on the sample preparation method and heat history. The samples synthesized by molten salt exhibit unique property. The spin glass behavior of slow-coolingε-Ga_1.1Fe_0.9O₃ sample is determined by ac susceptibility, and the exchange bias effect and traning effect are also observed.A rhombohedralα-Ga_1.2Fe_0.8O₃ has been successfully prepared by high pressure and high temperature technique usingε-Ga_2-xFe_xO₃ as precursor. It has been found thatα-Ga_1.2Fe_0.8O₃ crystallizes in a rhombohedral structure with space group R(3|-)c, and the lattice parameters area=5.0137(A|。) , c=13.5594(A|。). The Raman active modes ofα-Ga_1.2Fe_0.8O₃ compound are corresponding to those ofα-Fe2O₃ andα-Ga₂O₃. The Raman active mode at 660 cm-1 indicates the formation of lattice distortion. The lattice thermal expansion coefficient of theα-Ga_1.2Fe_0.8O₃ in the range of room temperature-800oC have been found to beα_a=9.96×10^-6K^-1,α_c=1.2×10^-5K^-1, exhibiting anisotropy.The deviation between FC and ZFC magnetization and the unsaturated hysteresis loop even at 50kOe field forα-Ga_1.2Fe_0.8O₃ compound indicate the existence of frustration effect, and the spin glass behavior is unambiguously confirmed by ac susceptibility measurement. The dependence of ZFC magnetization on waiting time is observed. The step-like behavior around stop-temperature in the heating and cooling FC magnetization indicates that the system keeps a memory imprinted in the FC process. The difference between the reference ZFC magnetization and waiting ZFC magnetization shows a dip around the stop temperature, and the splitting between them is not restricted only to the vicinity of stop temperature. The glassy behavior of theα-Ga_1.2Fe_0.8O₃ compound can be ascribed to both the common frustration, from the bond anisotropy, and the randomness resulting from the random distribution of Ga/Fe ions.