The Preperation, Electronic Transport And Magnetic Properties Study Of Composite Multiferroics

The development of magnetic materials and electronic materials has penetrated in all areas of modern technology, and the devices miniaturization trend has led to the development of multifunctional materials which can integrate electric and magnetic properties. Multiferroics is such a versatile material and attracts more and more attention. Multiferroic material has not only a single ferroics (such as ferroelectricity, ferromagnetism), but also some new effects by the coupling of single ferroics which greatly widened the scope of application of ferroics material. Ferromagnetic-ferroelectric composite material is one of the categories and the most typical representation of such multiferroic materials which not only possess ferroelectricity and ferromagnetism, but also produce a special magnetoelectric effect.In this paper, based on the achievements of transition metal oxides study in our laboratory, we prepared ferroelectric-ferromagnetic composite multiferroic materials by high-temperature solid-phase reaction method, and their electrical properties and magnetic properties were characterized, trying to find ferromagnetic-ferroelectric composite materials which can be used in higher temperature range.1. The preparation, structure and DC magnetization of ErMnO₃The single phase multiferroics ErMnO₃ is successfully prepared by solid-state reaction method. Its crystal structure, morphology and DC magnetization have been characterized. The anti-ferromagnetic transition temperature is about 80K.The results show that, ErMnO₃ is a multiferroics, which possesses both ferroelectricity and antiferromagnetism below 80K. Because the temperature is far lower than room temperature, the single-phase multiferroics can not be used in practical application.2. The preparation, resistivities and DC magnetization of composite multiferroicsThe composites (x) La_5/8Ca_3/8MnO₃ + (1-x) ErMnO₃ are successfully prepared by solid-state reaction method. Their crystal structure, morphology, resistance and DC magnetic properties were characterized. When the ferromagnetic phase content x≥ 40%, the conductive properties of the samples are similar to that of the ferromagnetic phase, which can be explained using percolation theory model. DC magnetic susceptibility results show that the magnetization of composites is stronger in a wider temperature range compared with the single phase multiferroics ErMnO₃.3. The resistivity properties and DC magnetization of Sm_0.90Nd_0.10CdThe single phase polycrystalline intermetallic compounds Sm_0.90Nd_0.10Cd is prepared by induction melting. The electrical resistivity and magnetic properties were studied at low temperatures. The results show that the magnetic compensation temperature (T_comp) has something to do with thermal history and the magnitude of the external magnetic field. The T_comp shifts to the lower temperatures with increasing the applied field, showing strong magnetic field dependence. The alteration of the T_comp has much to do with the field-induced flipping of the spin and orbital moments under the higher magnetic field, making the spin-orbital magnetic compensation temperature shifting to the lower temperature, and thus give rise to the phenomenon of zero magnetization. This experiment result contributes to understand the physical nature of Sm intermetallics.