| The materials can be called multiferroic materials if two or more primary ferroic order parameter (such as, ferromagnetism, anti-ferromagnetism, ferroelectricity anti-ferroelectricity and ferroelasticity) can coexist in one kind of material. Multiferroic materials have exhibited extraordinary physical interpretation and potential applications in spin quantum devices, data accessors and detectors. In recent decades, multiferroic materials have been a hot spot in research throughout the world. In order to urge the multiferroic materials to be applied in actual life, the following conditions must be satisfied:(1) strong magnetoelectric coupling,(2) ferromagnetism and ferroelectricity coexisted in one kind of material and (3) the temperature of ferroelectric phase transition and ferromagnetic phase transition stay at room temperature or above. At present, this kind of multiferroic materials is inexistence. BiMnO3and BiFeO3are widely considered as multiferroic materials. However, BiMnO3has weak magnetoelectric coupling and low temperature of ferromagnetic phase transition (about100K). BiFeO3exhibits weak anti-ferromagnetism property.In this paper, we prepare our sample NKBT by sol-gel method and SmFeO3by solid state sintered technology. Then, we study the corresponding properties of NKBT and SmFeO3.(1) The sample (Na1-xKx)0.5Bi0.5Ti03(x=0,0.04,0.06,0.08,0.3) which has orthorhombic perovskite structure were prepare by sol-gel method and study their properties of ferroelectricity, ferromagnetism and magnetoelectric coupling. The X-ray diffraction patterns of (Na1-xKx)0.5Bi0.5TiO3(x=0,0.04,0.06,0.08,0.3) annealed at800℃indicate that (Na1-xKx)0.5Bi0.5TiO3(x=0,0.04,0.06,0.08,0.3) have a single phase with orthorhombic perovskite structure. The magnetism of sample (Na1-xKx)0.5Bi0.5TiO3(x=0,0.04,0.06,0.08,0.3) reduce with the increasing temperature and increasing sintering time. The samples exhibit diamagnetism when the samples are annealed at1000℃for2hours. Then, we treated our samples in a vacuum. The results revealed that the existence of oxygen vacancy could prevent ferromagnetism. With the increasing x, the magnetism reduces and the remanent polarization increases. The magnetodielectric effect of (Na1-xKx)0.5Bi0.5TiO3(x=0,0.04,0.06,0.08,0.3)have high sensitivity in the condition of low frequency. However, the magnetodielectric effect becomes weak with the increasing x. Finally, the sample (Na1-xKx)0.5Bi0.5TiO3(x=0,0.04,0.06,0.08,0.3)are treated in electric field for1hour. Our results reveal that the magnetism of our sample increases with the increasing electric field. In a word, the sample (Na1-xKx)0.5Bi0.5TiO3(x=0,0.04,0.06,0.08,0.3) are multiferroic materials at room temperature.(2) We prepared the sample SmFeO3by solid state sintered technology. The sample has a single phase with orthorhombic perovskite structure. We obtain the M-T curve of SmFeO3in different magnetic field at room temperature. Same trend are observed in the temperature-rise period and temperature-rise period. Without magnetic field, magnetic moments decreased monotonously with the increasing temperature. With certain magnetic field, magnetic moments increase gradually, undergoes a maximum, and then decreases with the increasing temperature. The peak appear at275K for H=300Oe and175K for H=2000Oe. The results indicate that SmFeO3exhibit ferromagnetism. With magnetic filed H=300Oe, the curves of magnetization as a function of magnetic filed under/without10kV/cm electric field parallel to the magnetic field were measured at room temperature and we observed an increase of magnetization when the electric field was introduced. We also found same results under the condition of square wave electric fields perpendicular to the magnetic field H at room temperature. The results indicate that the electric field can controlled magnetization successfully. |
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