Bi5Fe0.5M0.5Ti3O15(M=Cr,Mn)室温多铁薄膜磁--电性能研究

Multiferroics not only exhibit simultaneously both magnetic and ferroelectric orders, but also there is a coupling between the two orders which enables the electric control of magnetism and vice verse. Therefore, multiferroics have been widely studied for their potential applications in multi-state memory. Recently, the four-layered perovskite multiferroics have been widely concerned because of their coexistence of magnetism and ferroelectricity at room temperature, and the multiferroelctric properties may be enhanced by the interaction between different magnetic ions. However, the mechanism of the magnetism and magnetoelectric effects are not clear. To solve the above problems, the following experimental will be explored. We will utilize the chemical solution deposition (CSD) to fabricate the Bi5Fe0.5M0.5Ti3O15(M=Cr,Mn)thin films. The influence of interaction between the magnetic ions with different electron configuration on ferroelectricity, magnetic properties , and magnetoelectric effects will be studied. Then different oriented BFMO thin films will be deposited by adjusting process and different kind of substrates to explore the impact of orientation and stress on the magnetism and magnetoelectric effect. The influence of orientation and stress on magnetic and magnetoelectric properties will be studied. All these will be done to not only discuss the mechanism of magnetic and magnetoelectric but provide a scientific basis for the improvement of multiferroictricity and for their device application.

多铁性材料不仅同时具有铁电性和磁性，而且两者之间存在耦合，可以实现磁－电相互调控，在多态器件方面有着潜在的应用前景。对四层层状钙钛矿多铁材料的研究发现，不同的磁性离子耦合能明显改善样品室温下的铁电性和磁性，但磁性能的起源和磁电相互作用机制等问题还没形成统一的认识。针对以上问题，本项目拟用湿化学法制备四层层状钙钛矿Bi5Fe0.5M0.5Ti3O15 (M=Cr,Mn)薄膜，研究不同电子构型磁性离子之间的相互作用对材料磁性、铁电性及磁电效应的影响。同时通过调整制备工艺和选择不同的衬底，改变薄膜的取向和应力，研究取向和应力等对薄膜磁性和磁电效应的影响。探讨四层层状钙钛矿材料中的磁性和磁电相互作用等机制，为提高层状钙钛矿的多铁性提供实验依据。

单一功能材料已经不能满足功能多样化实际应用的需要，探索多功能化材料是未来科技发展的必然趋势。层状钙钛矿氧化物因其特殊的晶体结构可以在单相体系中实现多种参量的共存和耦合，成为研究热点。本项目原计划是制备Bi5Fe0.5M0.5Ti3O15 (BFMT, M = Cr, Mn)薄膜并研究其多铁性，在实际实施中，制备出的两种BFMT薄膜尽管其铁电性良好，而室温下表现为顺磁性，因此我们将原计划中的Cr/Mn改成Ni，并从提高层状氧化物磁性能的角度开展了以下工作：(1) 对四层结构的Bi5FeTi3O15 (BFTO)进行A/B位掺杂改性研究，研究发现，少量Ni掺杂(BFNT)能有效提高材料的磁转变温度，BFNT室温下呈弱铁磁性且有良好的铁电性。同时BFNT纳米材料有良好的光催化性质，Ni掺杂不仅可以提高可见光的光催化效率，且可以实现催化后的磁回收，避免材料对水体造成二次污染。在Co掺杂的BFTO (Bi5Fe0.5Co0.5Ti3O15: BFCT)的基础上用镧系元素对A位进行掺杂改性，发现A位掺杂能够进一步提高磁性，原因是A位掺杂能进一步倾斜Fe-基和Co-基次晶格。特别有意义的是，在Gd掺杂的BFCT样品中发现了磁介电现象，在190 K—280 K, 在0.7 T 磁场作用下，MDC可达到1.8 %，分析其磁介电为本征行为。(2) 为进一步提高材料的磁性，我们用增加磁性离子层的方法，对五层层状钙钛矿进行B位掺杂改性研究。研究发现，增加磁性离子层是一种有效地提高材料磁性的方法，同时在A位用Sr取代Bi能有效提高材料的铁电性能。上述研究结果，为层状钙钛矿氧化物的在多功能复合及调控方面提供了实验依据。