| Multiferroic materials can be divided into single-phase multiferroic compounds and composite multiferroic materials. Since the multiferroic material was first discovered, there are kinds of multiferroic compounds which have been found. However, among several decades, the study of the single-phase multiferroic materials has been in the low tide. Over the past decade, the single-phase multiferroic materials have attracted widespread attention. Rare earth manganese oxides and bismuth ferrite multiferroic materials are the representative of several single-phase multiferroic material systems. Since the ferromagnetic transition temperature and ferroelectric transition temperature of the multiferroic materials is relatively low, or the magnetoelectric coupling effect is very weak in the multiferroic materials, the multiferroic materials can not meet the actual application. It is the key issues to be solved that the new room temperature single-phase multiferroic material, the enhanced magnetoelectric coupling effect and the understanding of the microscopic physical mechanisms.Our research focuses on the study of the ion doped YMnO3 and BiFeO3. Compared to previous studies on YMnO3 and BiFeO3, based on the synchrotron radiation X-ray absorption spectrum, this work explains the change of the electrical and magnetic properties of the ion doped YMnO3 and BiFeO3 by analyzing local structure and the electronic hybridized orbit.Firstly, to study the influence of Fe3+ion doped YMnO3 on MnO5 trigonal bipyramidal structure and the ferromagnetism of YMnO3, polycrystalline YMn1-xFexO3 (0?x?0.08) samples were prepared by a standard solid-state reaction. By changing the concentration of Fe3+ ion, we have studied the change of O 2p-Mn 3d hybrid electronic state. The lattice structure of hexagonal YMnO3 unchanged with Fe3+ doped. The magnetic properties of YMn1-xFexO3(0?x?0.08) samples are enhanced attributed to doping Fe3+ ion in YMnO3. Doped Fe3+ ions relieve the frustration effect of YMnO3, destroy the superexchange interaction between Mn3+, and induce the competition between different magnetic interactions. According to the O K edge's and Mn L edge's XAS absorption spectra of YMn1-xFeO3(0?x?0.08) samples, it can be obtained that there are more empty electronic states in the O 2p-Mn 3d hybrid orbitals as Fe3+ ion doped, which indicates the change of the O 2p-Mn 3d hybrid orbitals. The change of the hybrid orbitals can cause the change of chemical bonding and MnO5 trigonal bipyramidal structure, causing the change of the ferromagnetism of YMnO3.Secondly, to study the influence of ions doped BiFeO3 on the magnetic properties and local microstructures, polycrystalline BiFeO3, BiFe0.95Mn0.05O3 and Bi0.90La0.10FeO3 samples were synthesized via sol-gel method. The positions of Bi3+, Fe3+in BiFeO3 are respectively replaced by Mn3+, La3+. The lattice structure of BiFeO3 has not been changed by doping Mn3+, La3+ions. It still is distorted perovskite structure. With La3+ ions doping, the ferromagnetism of BiFeO3 has not been changed visibly. Conversely, Mn3+ions replacing the position of Fe3+ ions enhance the ferromagnetism of BiFeO3. According to the Fe L edge's XAS absorption spectra, the dopant of La3+and Mn3+ions do not lead to the emergence of Fe2+. The O K edge's XAS absorption spectra illustrates that there are more empty electronic states in t2gand eg hybrid orbitals with Mn3+ions doping. The change of electronic states also illustrates the change of the O 2p-Fe 3d hybrid orbitals, thereby affecting the bond lengths and bond angles of Fe-O-Fe, the magnetic moment orientation of Fe3+ions and the ferromagnetism of BiFeO3. The suppressed cycloid antiferromagnetic order leads to the presence of spatial inversion symmetry breaking and time inversion symmetry breaking simultaneously, thereby enhancing the magnetoelectric coupling effect of BiFeO3. |
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