激发态电荷转移有机体的多铁性研究

随着人们对多铁性的深入了解,越来越多不同类型的有机多铁材料被合成出来.激发态电荷转移有机体的电荷转移网络是由一个提供电子的分子(给体donor,D~+)和一个接受电子的分子(受体acceptor,A~-)有序排列后构成的.D~+A~-长程有序排列,其激发态(激子)具有较长寿命和±1/2自旋,这是产生室温铁电性和铁磁性的根本原因.激发态容易受外场刺激,因此光照、磁场、电场、应力等能够很好地调控这类材料的铁电极化、磁矩和相应的磁电耦合系数.激发态电荷转移有机体不仅大大丰富了室温多铁材料体系,而且可以为开发新型多功能电子器件提供材料基础和技术储备.

Excited charge-transfer organics with multiferroicity

Multiferroics, showing simultaneous electric and magnetic degree of freedom, has aroused increasing interest due to tailored multiferroic properties and magneto-electric coupling for shaping the development of energy-efficient multifunctional devices. Now, the multiferroics can be classified as two groups:1) inorganic multiferroics, which can be single-phase, multi-phases oxide multiferroic or multiferroic heterojunction and 2) organic counterpart, which is mostly determined by instinct charge-transfer behavior. But it is difficult to find the polarization and the magnetization co-exist in a single-phase oxide multiferroic material, and their coupling range in the multiferroic heterojunction is only several atomic layers, which limits the applications. As a result, more and more different types of organic multiferroics have been studied. Some organic complexes can display dual ferroelectric and ferromagnetic properties at ambient temperature, e.g. thiophene-fullerene donor-acceptor charge-transfer networks. The organic charge-transfer complex is based on electron donor (D⁺) and acceptor (A^-) assembly. D⁺A^- are long-range ordering, the excitons have μs lifetime and ±1/2 spin, which contributes to the room temperature ferroelectricity and ferromagnetism. The excitons can be excited by external magnetic field, electric field, illumination and stress, and eventually influence the polarization, magnetization and magnetoelectric coupling coefficient. However, there are still many problems to be solved, i.e., searching for new charge-transfer systems and preparing supramolecular co-crystal with ordered molecular chain, further improving magnetoelectric properties; developing the heterojunction technology and epitaxial growth of organic ferroelectric or ferromagnetic systems on excited organic films, which is expected to greatly improve their magnetoelectric coupling effects; inventing more new charge transport organic multiferroic devices to extend the application scope of new multiferroic devices in actual industrial production. Generally speaking, the organic charge-transfer complexes not only greatly enrich the room temperature multiferroics materials, but also provide the technical basis for developing the new multifunctional electronic devices.