铋层状氧化物单晶薄膜多铁性研究进展

室温单相多铁材料非常稀缺,磁性元素掺杂的铋层状钙钛矿结构Aurivillius相氧化物是一类重要的单相室温多铁材料,但由于缺少单晶类样品,这一类多铁材料研究主要是围绕多晶类块体或者多晶薄膜展开,它们的磁、电等性能研究大都采用宏观探测方式,因此这类多铁材料的多铁性机理研究进行得非常困难.近年来在高质量单晶薄膜的基础上,研究了多种磁性元素掺杂和不同周期结构的铋层状氧化物多铁单晶薄膜.这些单晶薄膜在室温下大都具有层状面面内方向的铁电极化,以及比较小的室温磁化强度,低温区存在第二个磁性相变.通过X射线共振非弹性散射实验发现元素掺杂会改变金属和氧原子之间的氧八面体晶体场的劈裂,能够增强铁磁性.另一方面,通过极化中子反射实验发现薄膜主体的磁化强度远小于通常探测的宏观磁化强度,说明单晶薄膜中磁的来源及其磁电耦合机理和多晶块体很可能是不同的.铋层状单晶薄膜的多铁性对未来继续改善这类材料的多铁性能有很好的指导作用.     

Growth and transport properties of topological insulator Bi_2Se_3 thin film on a ferromagnetic insulating substrate

Exchange coupling between topological insulator and ferromagnetic insulator through proximity effect is strongly attractive for both fundamental physics and technological applications. Here we report a comprehensive investigation on the growth behaviors of prototype topological insulator Bi_2Se_3 thin film on a single-crystalline LaCoO_3 thin film on SrTiO_3 substrate, which is a strain-induced ferromagnetic insulator. Different from the growth on other substrates, the Bi_2Se_3 films with highest quality on LaCoO_3 favor a relatively low substrate temperature during growth. As a result, an inverse dependence of carrier mobility with the substrate temperature is found. Moreover, the magnetoresistance and coherence length of weak antilocalization also have a similar inverse dependence with the substrate temperature, as revealed by the magnetotransport measurements. Our experiments elucidate the special behaviors in Bi_2Se_3/LaCoO_3 heterostructures,which provide a good platform for exploring related novel quantum phenomena, and are inspiring for device applications.