Study On Preparation And Properties Of A New Kind Of Multiferroics Manganites Of Mn-site Doping

Single phase multiferroics have attracted much attention due to the simultaneous existence of ferroelectricity and magnetism,being prone to achieve the magneto-electric coupling.According to the micromechanism of inducing ferroelectricity,the single phase multiferroics were classified into two categories.The origin of ferroelectricity of type-I multiferroics is not related to the magnetism.This type generally shows the high ferroelectric and magnetic Curie temperature.On the other hand,the type-II multiferroics is considered to refer to some specific magnetic orders.Due to the ferroelectricity is correlated to the magnetic spin,the type-II multiferroics have the intrinsic and prominent magneto-electric mutual interaction.However,most of the type-II multiferroics show up small magnetic moment,low ferroelectric Curie temperature,and weak polarization.Therefore,improving the transition temperature and polarization with high magnetoelectric coupling becomes the main aim to achieve.The lattice structure and magnetism of polycrystalline CaMn_7-xGa_xO₁₂?x=0,0.1,0.2,0.3,0.4?synthesized by solid state method have been investigated.The refined x-ray diffraction patterns show that a well single phase Ga doped CaMn₇O₁₂ crystals can be obtained by solid state method and their lattice structure is rhombhedral with R-3.The lattice parameter a linearly decreases while parameter c linearly increases with increasing doping concentration,leading to a lattice distortion.Magnetic susceptibility and inverse susceptibility as a function of temperature show that CaMn_7-xGa_xO₁₂ and undoped CaMn₇O₁₂ behave the basically identical magnetic characterization,that is,there are two magnetic phase transitions at 90 K and 40 K.And the antiferromagnetic transitional temperature is not obviously influenced by non-magnetic Ga ions doping.However,the magnetization at temperature lower than 40 K is enhanced and there is a new transitional temperature point observed at temperature range between 40 K and 90 K,which indicates that Ga ions participate into the magnetic interaction.