多铁性M-型六角铁氧体材料的制备与磁电响应

Multiferroic material integrates ferroelectricity and ferromagnetism into one structure, which provides more broad freedoms for multiple functionality of a single electric device. It keeps itself as one of the frontier and hot topics in materials science. This project will mainly focus on the investigation of ferroelectric、magnetic and magnetoelectric properties of M-type hexaferrites. First of all, fine powders of M-type hexaferrites will be controllably fabricated by a polymer precursor method. The powders will then be pressed into a pellet, which will be sintered into ceramics at different temperatures. Thin films of M-type hexaferrites will be prepared by sol-gel process. Both ceramic and thin film specimens will be annealed in O2 atmosphere for several times so as to remove oxygen vacancies and transform Fe2+ into Fe3+. The ferroelectricity, ferromagnetism and magnetoelectric properties of the specimens will be investigated systematically. Further research work will be carried out on the effect of external magnetic fields to the ferroelectricity and dielectric properties of M-type hexaferrite specimens as well as magnetic polarization behavior induced by electric field. We will then investigate the pinning function of rare earth ions on the cycoidal conic spins in M-type hexaferrites. The electronic structure, spin-orbit interaction and their impact on macroscopic magnetoelectric properties will also explored. Combining the crystal and magnetic structure models, we will be able to further disclose the origin of the ferroelectricity and physical mechanism of magnetoelectric coupling effect in M-type hexaferrites. The successful implement of this project will enrich the fabrication methods and species of multiferroic materials. The fruit outcomes of this investigation will provide new insight into the design of new types of multiferroic materials as well as integration of multiferroic thin films with semiconducting electric circuit.

多铁性材料集铁磁性和铁电性于一体，为器件的多功能化提供了更广阔的自由度，是材料科学前沿问题之一。本项目将通过聚合先驱物的方法制备M-型铁氧体精细粉体，将之烧结成陶瓷；同时用溶胶-凝胶方法制备薄膜样品；之后将陶瓷和薄膜样品在氧气下退火，以消除样品内的氧空位并将Fe2+氧化为Fe3+。系统地研究M-型六角铁氧体的铁电、铁磁和磁电耦合性能；研究铁氧体材料在不同磁场下的铁电行为；探索不同偏压下铁氧体材料的磁极化现象。探究稀土离子对锥型自旋的钉扎作用，揭示M-型六角铁氧体材料的电子结构、自旋轨道偶合和宏观磁电性能之间的关系；结合晶体结构和磁相结构模型，进一步揭示M-型六角铁氧体铁电性的起源及磁电耦合的物理机制；通过本项目的研究可以丰富多铁性材料的制备方法，对多铁性材料与半导体电子线路的集成、开发室温单相多铁性材料将具有重要意义。可以为发展多铁性信息存储器、电子自旋器件的技术提供重要的理论和实验依据。

1）通过氧气退火，使BaFe12O19陶瓷在室温下的电滞回线达到了饱和，实现了SrFe12O19和BaFe12O19室温下的铁电性，使之与铁磁性共存，从而证实了M-型铁氧体SrFe12O19和BaFe12O19的多铁特性。实现了两种材料的磁电耦合效应。 .2）发现了La0.2Sr0.7Fe12O19和SrFe12O19两种化合物的磁性半导体特性；实验上实现了其光催化降解甲基蓝的过程，磁性催化剂可回收重复使用，避免了催化粉体对环境的二次污染。说明这类化合物可以应用于光催化降解有机染料或其他有机污染物，具有应用于环境保护领域的潜力；另外，磁性半导体特性为M-型六角铁氧体用作集运算与存储于一体的新型芯片提供了契机。 .3）通过掺杂并调整La离子的浓度，实现了LaxSr1-xFe12O19从铁电性(x=0)调谐到反铁电性（x=0.5）的过程; 开发了一种集反铁电性与铁磁性于一体的新型单相多铁性材料；发现了La0.5Sr0.5Fe12O19的巨磁电容效应与巨磁阻效应；具有重要的科学意义。对未来实现多铁性材料在电写磁读存储器中的应用打下良好的理论和技术基础。.4）以安德森模型构建哈密顿量，理论研究了三角晶格结构的磁阻挫对多铁性材料电荷输运性质的影响规律；计算结果表明，在有限温度下，当其他相互作用常数不变时，随着温度的升高，三角晶格阻挫结构的近藤峰会被抑制，说明电导会温度的升高而下降。当温度进一步升高，近藤峰和RKKY峰均消失。

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