Medle Rupnik Peter, Lisjak Darja, Čopič Martin, Čopar Simon, Mertelj Alenka
Jožef Stefan Institute, Ljubljana, Slovenia.
Department of Physics, Faculty of Mathematics and Physics, University of Ljubljana, Ljubljana, Slovenia.
Sci Adv. 2017 Oct 6;3(10):e1701336. doi: 10.1126/sciadv.1701336. eCollection 2017 Oct.
One of the advantages of anisotropic soft materials is that their structures and, consequently, their properties can be controlled by moderate external fields. Whereas the control of materials with uniform orientational order is straightforward, manipulation of systems with complex orientational order is challenging. We show that a variety of structures of an interesting liquid material, which combine chiral orientational order with ferromagnetic one, can be controlled by a combination of small magnetic and electric fields. In the suspensions of magnetic nanoplatelets in chiral nematic liquid crystals, the platelet's magnetic moments orient along the orientation of the liquid crystal and, consequently, the material exhibits linear response to small magnetic fields. In the absence of external fields, orientations of the liquid crystal and magnetization have wound structure, which can be either homogeneously helical, disordered, or ordered in complex patterns, depending on the boundary condition at the surfaces and the history of the sample. We demonstrate that by using different combinations of small magnetic and electric fields, it is possible to control reversibly the formation of the structures in a layer of the material. In such a way, different periodic structures can be explored and some of them may be suitable for photonic applications. The material is also a convenient model system to study chiral magnetic structures, because it is a unique liquid analog of a solid helimagnet.
各向异性软材料的优点之一是其结构以及相应的属性能够由适度的外部场来控制。对于具有均匀取向有序性的材料，其控制较为直接，而对于具有复杂取向有序性的系统进行操控则具有挑战性。我们表明，一种有趣的液体材料，它将手性取向有序性与铁磁取向有序性相结合，其多种结构能够通过小磁场和电场的组合来控制。在磁性纳米片悬浮于手性向列型液晶中时，纳米片的磁矩沿液晶的取向排列，因此该材料对小磁场表现出线性响应。在没有外部场的情况下，液晶的取向和磁化具有缠绕结构，根据表面的边界条件和样品的历史情况，这种结构可以是均匀螺旋的、无序的或呈复杂图案有序排列。我们证明，通过使用小磁场和电场的不同组合，可以可逆地控制材料层中结构的形成。通过这种方式，可以探索不同的周期性结构，其中一些可能适用于光子应用。该材料也是研究手性磁结构的便利模型系统，因为它是固体螺旋磁体独特的液体类似物。
