螺旋自旋序多铁氧化物在多场调制下的宽域介电响应

Helix spin multiferroics, whose peculiar helix spinwave order can induce a strong intrinsic magnetoelectric coupling, would be considerable potential applications in multi-states information memory and magnetic sensor devices. However, up to now, the microscopic mechanisms behind magnetoelectric couplings and magnetocapacitance effects in strong spin-electrical polarization correlated oxides have still been unclear. Utilizing board band dielectric responses of helix spin multiferroics under multi-fields(electric, magnetic and thermal fields), this project intends to explore the effects of spin order transitions on electrical polarization states; establish the mechanisms of generations, transport and relaxations of magnetic-driven-dipoles, charge carriers and defects at low frequency; gain the behavior rules of soften optical phonon, spin-phonon or spin-lattice couplings related elementary excitations in the multi-fields in the infrared-terahertz band; and obtain its the electronic energy band structures and the regular of electron interband transitions under multi-fields in ultraviolet-near infrared band. This project, focused on the dielectric responses of various polarization/spin mechanisms to broad band electromagnetic wave, not only can favor deeply understandings of the microscopic nature of magnetoelectric and magnetocapacitance effects in strong spin-electrical polarization correlated oxides, but also can provide guide information for the development of multiferroic devices.

螺旋自旋序多铁材料具有奇特的螺旋状自旋波有序可诱导出内禀的强磁电耦合效应，故而其在多态信息存储和磁传感器件中有着广泛的潜在应用。然而，目前螺旋自旋序多铁氧化物中磁电耦合效应特别是巨磁电容效应起源的微观机理尚不清晰。本项目拟通过研究多场（温场、磁场、电场）调制下的螺旋自旋序多铁材料的宽域（低频、光频）介电响应来探索其自旋序相变对电极化状态的影响规律；建立低频下磁致电偶极子、载流子、缺陷的弛豫、输运动力学；获得远红外-太赫兹频段下自旋-声子耦合、电子-声子耦合和光学软模等相关的元激发受外场调制的变化规律；探索多场调制下紫外-近红外频段价电子跃迁规律，确定其电子能带结构。本项目研究多场下各种自旋/极化机制对宽域电磁波的介电响应不仅有助于多角度综合地理解螺旋自旋序多铁氧化物中磁电耦合和磁电容效应的微观本质，也为多铁相关器件的研制提供有益的理论和实验指导。

螺旋自旋序多铁材料具有奇特的螺旋状自旋结构可诱导出内禀的强磁电耦合效应，故而其可在多态信息存储和磁传感器中有潜在应用。本项目研究围绕着包括螺旋自旋序多铁在内的若干多铁材料微结构对介电响应的影响规律；自旋序对电极化状态的影响规律；多铁材料中载流子、缺陷产生机制以及弛豫、输运机制；铁性材料中元激发、电子能带跃迁及电子能带结构等方面展开。项目实施过程中，成功制备了一系列DyFeO3 (DFO)、Ba0.5Sr1.5Zn2Fe12O22 (BSZFO)、BaFe12O19 (BFO)、Bi5Ti3FeO15 (BTFO)、SrMnO3 (SMO)、BaTiO3/(La,Ca)MnO3 (BTO/LCMO)等具有螺旋磁序，晶格-自旋耦合及天然超晶格共生Aurivillius单相多铁材料及若干铁电/铁磁异质结；获得了BSZFO、 BFO、 BTFO 、BTO/LCMO微结构尤其晶粒/晶界界面、薄膜/衬底界面、薄膜/电极界面等微结构对介电响应的影响规律；发现M型六角铁氧体多晶低温下呈量子顺电态；在 DFO多铁材料中建立Dy-Dy反铁磁自旋序及自旋重取相变与电极化关联从而在证实在该材料体系中具有很强的晶格-自旋相互作用；获得螺旋磁序、晶格-自旋耦合及Aurivillius层状多铁材料中氧空位、变价Fe、Mn离子相关缺陷和缺陷复合物的弛豫及输运机制；通过等效电路模型等手段，提取出BTFO晶粒和晶界电学参数随温度场与磁场的演变过程，并证实BTO/LCMO磁介电效应来源于巨磁阻效应与界面空间电荷极化的联合效应，从而澄清若干Aurivillius层状多铁材料及铁电/铁磁异质结体系中磁介电效应的起源；通过亚矫顽场下的交流介电响应，揭示了(Pb,Sr)TiO3铁电薄膜在亚矫顽场下宏畴-纳米微畴的转变和热致畴壁解钉扎之间的相互竞争过程；通过介电频谱揭示SMO薄膜中氧空位和Jahn-Teller极化子的相互关联；获得若干铁性材料的电子-声子耦合、极化子元激发产生及输运动力学机制及带-带跃迁吸收及带尾吸收行为规律;通过B位掺杂扩宽六角铁氧体磁致铁电自旋相的范围及相变温度；证实氧空位和Mn4+-Mn3+之间的双交换作用会导致应力状态下的外延单晶(001)SMO超薄膜出现铁磁性。