Hexagonal Ferrite-Ferroelectric Core-Shell Nanofibers, Field-Assisted Assembly of Superstructures and Studies on Magnetoelectric Interactions

非技术摘要：纳米材料“通过设计”可以将磁场转换为电场，反之亦然。 自然界中能够进行这种场转换的材料非常少，并且它们中的大多数要么效率很低，要么只能在低温下起作用。 该项目侧重于工程纳米材料的基础物理学，分为两个阶段。一个是铁磁的，在施加的磁场中变形，另一个是铁电的，将这种变形转化为电场。 由于转换是严重依赖于两个阶段之间的表面接触，研究的重点是同轴纳米线具有更高的表面积，它们的体积比散装复合材料。 同轴光纤是通过一种称为静电纺丝的技术合成的，其特征在于场转换效率和灵敏度。 这些复合材料非常适合用作超灵敏的微型磁场传感器和阵列，用于成像应用，如心磁图（MCG）和脑磁图（MEG），这是诊断与心脏和大脑相关疾病的强大工具。 纳米材料还具有在信号处理和能量收集方面的应用潜力。 该研究的其他重要影响是高级材料合成和表征的各级人力资源开发。PI和Co-PI计划招募本科理工科专业学生参与研究。将招募高中学生，特别是妇女和少数民族学生参加研究。技术摘要：拟议的研究重点是基础物理和铁磁六角铁氧体和铁电锆钛酸铅（PZT）的同轴纳米线的合成，纳米结构组装成超结构的帮助下的磁场和/或电场，以及研究磁和电子系统之间的耦合的内在本质。 主要关注的是具有Y型或W型六角铁氧体的光纤，这是由于它们的高各向异性场和自磁偏置特性，这将产生强磁电（ME）耦合，而不需要外部偏置磁场。 具体任务如下。 (i)合成的核-壳纤维与（Ni，Zn）Y型或（Co，Zn）W型六角铁氧体，与Zn取代的铁氧体的选择，旨在控制磁序参数ME研究在低频和共振模式在一个宽的频率范围内，从1 Hz到110 GHz。 (ii)纳米复合材料和阵列的透射电子显微镜（TEM）和扫描探针显微镜（SMM），其中Lorenz-TEM和SMM研究计划用于成像纤维和界面的磁性，铁电和电磁参数。 (iii)在局部机械、电和磁激励下，对单个纳米线和组件的ME效应进行调查，以建立ME耦合强度、复合材料的对称性/连通性和场定向组装参数之间的相关性，并优化纳米复合材料的形态以实现最大ME响应。 (iv)场定向组装和ME相互作用在个别纳米复合材料和组件的数据比较建模。 总体而言，该研究不仅增强了对纳米材料中ME效应的基本理解，而且对传感器和信号处理以及能源设备的新系列也很有用。该奖项反映了NSF的法定使命，并被认为值得通过使用基金会的知识价值和更广泛的影响审查标准进行评估来支持。

Nontechnical Abstract: Nano-materials "by design" can be capable of conversion of a magnetic field into an electric field or vice versa. There are very few materials in nature capable of such field conversion and most of them have either poor efficiency or can function only at low temperatures. This project focuses on the fundamental physics of engineered nanomaterials with two phases. One is ferromagnetic that deforms in an applied magnetic field and the other a ferroelectric that converts this deformation to produce an electric field. Since the conversion is critically dependent on the surface contact between the two phases, the research focuses on coaxial nanowires with a much higher surface area-to-their volume ratio than bulk composites. The coaxial fibers are synthesized by a technique called electrospinning and characterized in terms of field conversion efficiency and sensitivity. These composites are ideal for use as ultrasensitive, miniature magnetic field sensors and arrays for imaging applications such as magneto-cardiography (MCG) and magneto-encephalography (MEG) that are powerful tools for diagnosis of disorders associated with the heart and brain. The nanomaterials also have the potential for applications in signal processing and energy harvesting. Other significant impacts of the research are human resources development at all levels in advanced materials synthesis and characterization. The PI and Co-PI plan to recruit undergraduate science and engineering majors for participation in the research. High school students, women and minorities in particular, are to be recruited to participate in the research. Technical Abstract: Proposed research focuses on fundamental physics and synthesis of coaxial nanowires of ferrimagnetic hexagonal ferrites and ferroelectric lead zirconate titanate (PZT), assembly of nanostructures into superstructures with the aid of magnetic and/or electric fields, and studies on the intrinsic nature of coupling between magnetic and electric subsystems. The primary focus is on fibers with Y- or W-type hexagonal ferrite due to their high anisotropy field and self-magnetic bias characteristics that will give rise to strong magneto-electric (ME) coupling without the need for an external bias magnetic field. Specific tasks are as follows. (i) Synthesis of core-shell fibers with (Ni, Zn) Y-type or (Co, Zn) W-type hexaferrites, with the choice of Zn-substituted ferrites aimed at control of magnetic order parameters for ME studies at low frequencies and at resonance modes over a wide frequency range, from 1Hz to 110 GHz. (ii) Transmission electron microscopy (TEM) and scanning probe microscopy (SMM) of nanocomposites and arrays, where Lorenz-TEM and SMM studies are planned for imaging the fibers and interfaces in terms of magnetic, ferroelectric, and electromagnetic parameters. (iii) Investigations of ME effects on individual nano-wires and assemblies under local mechanical, electrical and magnetic excitations to establish correlations among ME coupling strengths, symmetry/connectivity of composites, and field-directed assembly parameters, and optimize the morphology of the nanocomposites to achieve a maximum ME response. (iv) Modeling of field directed assembly and ME interactions in individual nanocomposites and assemblies for comparison with data. Overall, the research not only enhances fundamental understanding of ME effects in nanomaterials, but is also useful for a new family of sensors and signal processing and energy devices.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.