强磁场下铁锰基纳米结构生长调控及其磁行为高分辨成像

Nanostructures have excellent performances in many fields, but their growth mechanisms are unclear, which makes their design and controlled growth very difficult and limits their wide applications. Using magnetic field, an ideal directional field, to control the nanostructures’ growth and self-assembly and using magnetic force microscope (MFM) to investigate their magnetic structures, will be beneficial to gain magnetic field orientation mechanism and capture peculiar magnetic behaviors. However, the magnetic field has low energy, which is proportional to the square of its intensity. In the past, the available magnetic field has low intensity and hasn’t get sufficient attention, until the appearance of the superconducting magnet. The most efficient way to utilize the pore and the magnetic field of superconducting magnet is to directly insert reactor into the pore with liquid helium. However, there is a thermal insulation problem and this kind of reactor hasn’t been reported yet. We participated in solving this problem by using liquid nitrogen dual cooling curtain technology, and designed high-throughput reactors, which greatly increases the use efficiency of the superconducting magnet. Such reators were further improved and can be transplanted into 35T water-cooled magnets. In order to study the directing function of magnetic field on chemical reaction, FeMn-based nanostructures are preferred due to their good magnetic properties and easy control by magnetic field. We found that the magnetic field has great effects on the reaction rate, crystal growth and unit assembly. The high index polyhedrons, interwoven nanostructures and nanohelixes, synthesized previously, have special magnetic curves and urgently need to be observed by high resolution MFM. However, it is difficult to locate the probe on the micro-/nano- structures. We participated in developing a MFM with accurately locating technology in superconducting and water-cooled magnets, which can be used to explore the relationship between the microstructure and the change of magnetic structure. Many important achievements are expected to obtain in the predictive synthesis of nanostructures.

纳米结构性能优异，但生长机理不清，导致定向设计困难。用定向场磁场控制纳米结构取向生长和自组装，用磁力显微镜高分辨观测其磁结构，可获得磁场定向机制，捕获特异性磁行为。但磁场能量较低且与其强度平方成正比，过去磁场较弱，重视不足，直到超导磁体出现。最有效利用超导磁体孔径和磁场的方式是直接将反应器插入液氦孔道中，但存在隔热问题，这种装置尚无报道。我们利用液氮双冷帐技术解决了该问题，并集成了高通量反应能力，成量级提高磁体使用效率，还移植到35T水冷磁体中。研究磁控反应时，首选磁性强易受磁场调控的铁锰系纳米结构。我们发现磁场对其反应速率、晶体生长、基元组装影响很大。前期合成的高指数多面体、交织结构和纳米螺旋，其磁性曲线特异性明显，急需高分辨磁成像，但微纳结构的探针定位困难。我们参与研发了可准确定位的超导和水冷磁体磁力显微镜，可用于探索微结构与磁结构变化关联性。预计在纳米结构预见性合成上取得重要成果。

磁场作为一种无接触、稳定的定向场，将成为一种新的取向生长和自组装原动力。在本项目中，我们主要以铁锰系纳米结构材料为主要研究对象，研究超导强磁场在铁锰系纳米结构材料控制生长中的定向作用，设计合成各种纳米效应明显的纳米结构材料，探索强磁场下纳米材料的生长机制。在本基金的支持下，我们利用自制的适用于超导磁体中高通量水热溶剂热反应器，根据目标材料的特性，设计温和且易受磁场影响的合成反应，成功地将水热溶剂热反应引入到超导强磁体中去。通过调节磁场的梯度，对合成反应进程进行监测，深入研究磁诱导各向异性作用的机理和规律，发现强磁场对铁锰系纳米结构材料（特别是磁异性纳米结构）的反应方向、反应速率和晶体生长与排列方式都有很大影响，获得一些具有不同表面活性、不同生长方向或不同排列方式的铁锰系纳米结构材料，并探索了所得纳米材料的性质对结构的依赖性。在本基金的支持下，目前已发表或被接收SCI论文14篇，其中影响因子大于8的10篇。