正交稀土锰氧化物o-RMnO3内的多重铁电产生机制

The type-II multiferroics, in which magnetism and ferroelectricity coexist and are mutually coupled intrinsically, has been a research hotspot of physics and material science in recent years. As a model system for type-II multiferroics, orthorhombic rare earth manganites, o-RMnO3 (R=Gd－Lu) provides a good platform for enriching the contents of multiferroic physics and revealing the physical mechanism of magneto-electric coupling. The basic multiferroicity of o-RMnO3 appears to be governed by the Mn3+ magnetism, and the competition between R-Mn and R-R interaction also plays complex and important roles in the ferroelectricity generation mechanism. Therefore, it’s very important for us to study the complicated and interesting ferroelectricity generation mechanism of o-RMnO3. In the previous studies, we have found that suppression of the R-R interaction is always with enhancement of the R-Mn interaction, and helps to improve the ferroelectric polarization for DyMnO3 and HoMnO3. In this project, we intend to regulate the multiferroicity of o-GdMnO3 and o-TmMnO3 by fine-tuning R/Mn stoichiometry and external magnetic field experimentally, and use XRD, SEM, XPS, dielectric, pyroelectricity, magnetism and specific heat measurements to characterize the crystal structure and multiferroic properties,then clarify their ferroelectricities generation mechanism, finally achieve the goal of complementing the multiple ferroelectricity generation mechanisms for o-RMnO3 with different spin configurations, and providing thinking and evidences for designing novel multiferroics.

第二类多铁材料的铁电性与磁性在量子范畴内禀共存，其丰富的物理特性已成为物理学和材料学的一个研究热点。正交稀土锰氧化物o-RMnO3(R=Gd－Lu)作为一类典型的第二类多铁材料，为丰富多铁性物理和揭示磁电耦合机制提供一个良好平台。其基本多铁性质取决于Mn3+磁序，R-Mn与R-R交互作用的竞争对体系电磁性质也有重要影响，故阐明o-RMnO3铁电产生机制尤为重要。前期工作中，申请人在DyMnO3和HoMnO3中发现R-R交互作用的减弱伴随着R-Mn交互作用的增强，有利于增强体系铁电极化。本项目从实验探索角度，以XRD、XPS、介电、热释电、磁性、比热为主要表征手段，关注R/Mn窄限非化学计量比和外场对o-GdMnO3和o-TmMnO3多铁性能的调控，明确其多铁性机制和磁电耦合特性，结合前期工作完善不同磁序构型o-RMnO3的多重铁电产生机制和磁电调控规律，为设计新型多铁材料提供思路和依据。

正交稀土锰氧化物o-RMnO3(R=Gd－Lu)作为一类典型的第二类多铁材料，为丰富多铁性物理和揭示磁电耦合机制提供一个良好平台。本项目从实验探索角度，以XRD、介电、热释电、磁性、比热为主要表征手段，关注Gd/Mn窄限非化学计量比和外场对多晶o-GdMnO3多铁性能的调控. 研究表明多晶o-GdMnO3中A型反铁磁序和螺旋磁序共存，其中的铁电性与Mn3+螺旋序，R3+Neel温度TR以下Gd-Mn交互作用和Gd-Gd交互作用竞争紧密相关，并且Gd3+或Mn3+间隙离子和离子空位缺陷有利于Mn3+螺旋序的形成，Mn3+反占位缺陷妨碍Mn3+螺旋序的形成。结合前期工作，o-RMnO3的基本多铁性质取决于Mn3+磁序，R-Mn与R-R交互作用的竞争对体系电磁性质也有重要影响。R-Mn交互作用的增强和TR温度以下R-R交互作用相对R-Mn交互作用的减弱对体系铁电极化都起促进作用。外磁场作用下，o-RMnO3中的R-R交互作用最为脆弱，R-Mn次之，Mn-Mn最强，外磁场对o-RMnO3体系铁电性能都是抑制作用。作为补充，我们在亚铁磁尖晶石MnCr2S4中观察到了与非共线YK特殊磁序和磁致伸缩相关的铁电性，外磁场对极低温Y-K相铁电性具有极大的调制作用，并增强了Cr3+铁磁相变点TC附近的晶格畸变。