过渡金属氧化物表/界面磁性及其调控

Due to symmetry breaking, surface/interface usually owns unique physical properties. The coexistence of more than one degrees of freedom and more than one competitive mechanisms in transition metal oxides assigns abundant physical complications to surface/interface effects. However, most of the previous works for manganites,the typical magnetic oxides, focused on magneto-resistive properties, and the surface/interface magnetism was less considered for lacking of appropriate analysis techniques, despite its importance for both fundmental and applied researches. Based on the analyses of exchange bias and magnetic proximate effects, in the present project we will perform a comprehensive study on surface/interface magnetism. The mains concerns are similarities and differences of bulk and surface/interface magnetism for both ferromagnetic and anti-ferromagnetic manganites and other relevant oxides. Particular attention will be paid to the effects of magnetic transition, including collinear to non-collinear spin structure transition, on surface magnetism. It will be tried to manipulate surface/interface magnetism by interface engineering based on well controlled epitaxial growth technique. Through these works,we hope to find the key factors affecting surface/interface magnetism, address the similarities and differences of bulk and surface/interface magnetism and their correlation, find feasible approaches towards surface/interface magnetism engineering which may pave the way towards the design of novel oxide-based artificial materials/devices.

由于对称破缺，表界面常表现出独特的物理行为。过渡金属氧化物的多自由度、多竞争机制为表面效应注入了新物理内涵。以往锰氧化物工作多围绕磁电子输运及光电行为展开，由于缺少磁敏感量有效描述表界面磁状态，很少涉及表界面磁性，特别是反铁磁体系表面磁性。而过渡金属氧化物表界面磁性无论对基础科学还是对应用科学而言都具研究价值。以交换偏置及磁邻近效应分析为基础，本课题将围绕表界面磁性展开，重点关注：典型铁磁、反铁磁氧化物表面行为与体行为间的异同及关联，磁相变、磁畴结构重整以及热涨落对表界面磁性的影响，特别关注自旋结构共线-非共线磁相变及不同磁结构类型间相变的影响。通过表界面极性、层间磁关联调控探索表界面磁性改性的途径。研究目标是阐明表界面磁性和体磁性间异同及关联，揭示界面电荷转移、轨道择优取向对表界面磁性的影响规律，探索表界面磁性调控的有效途径，进而为氧化物人工结构材料、器件的设计铺平

由于对称破缺，表界面常表现出独特的物理行为。过渡金属氧化物的多自由度、多竞争机制为表面效应注入了新物理内涵。以往锰氧化物工作多围绕磁电子输运及光电行为展开，由于缺少磁敏感量有效描述表界面磁状态，很少涉及表界面磁性，特别是反铁磁体系表面磁性。而过渡金属氧化物表界面磁性无论对基础科学还是对应用科学而言都具研究价值。以交换偏置及磁邻近效应分析为基础，本课题围绕表界面磁性展开，重点关注：典型铁磁、反铁磁氧化物表面行为与体行为间的异同及关联，磁相变、磁畴结构重整对表界面磁性的影响。通过表界面极性、层间磁关联调控探索表界面磁性改性的途径。. 本课题实现了预定研究目标，揭示了表界面磁性和体间异同、界面轨道择优取向对表界面磁性的影响规律， 获得了几种表界面磁性调控的新原理技术，为磁性氧化物人工结构材料、器件的设计提供了新思路。主要结果包括: . （1）发现了反铁磁氧化物BiFeO3表面的铁磁临近效应,并揭示了表面铁磁性随温度的变化规律;（2）发现了不同温度下温度梯度导致的铁磁绝缘体向非磁金属自旋流注入的新规律；（3）通过精心设计界面结构、磁结构，成功得到了层内铁磁耦合、层间反铁磁耦合的新型磁性氧化物超晶格，为多功能新材料、新物理效应研究拓展的新空间；（4）在两绝缘氧化物界面上成功获得了高导电二维电子气，并首次发现了比常规场效应高近两个量级的光电协同场效应；（5）通过在上述界面引入磁性缓冲层，成功获得了磁性与导电性共存的二维界面，这一工作为具有奇异物理效应的界面相研究提供了新思路、拓展了新空间。