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“经过设计”能够将磁场转化为电场，反之亦然。自然界中能够进行这种场转换的材料很少，而且大多数材料要么效率很低，要么只能在低温下发挥作用。本项目的重点是工程纳米材料的基础物理分两个阶段。一种是在外加磁场中变形的铁磁体，另一种是将这种变形转化为电场的铁电体。由于转化率严重依赖于两相之间的表面接触，因此研究的重点是具有比表面积与体积比远高于块体复合材料的同轴纳米线。同轴光纤是通过一种称为静电纺丝的技术合成的，并从场转换效率和灵敏度方面进行了表征。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，用于心磁图(MCG)和脑磁图(MEG)等成像应用，这些应用是诊断与心脏和大脑相关的疾病的强大工具。纳米材料还具有在信号处理和能量采集方面的应用潜力。这项研究的其他重大影响是在先进材料合成和表征方面各级的人力资源开发。PI和Co-PI计划招募本科生理工科专业的学生参与研究。高中生，特别是女性和少数民族，将被招募参与这项研究。技术摘要：拟议的研究重点是铁磁六方铁氧体和铁电锆钛酸铅(PZT)同轴纳米线的基础物理和合成，利用磁场和/或电场将纳米结构组装成超结构，以及研究磁子系统和电子系统之间耦合的内在本质。Y型或W型六方铁氧体纤维由于其高的各向异性磁场和自磁偏置特性，将在不需要外部偏置磁场的情况下产生强烈的磁电(ME)耦合。具体工作如下。(I)合成具有(Ni，Zn)Y型或(Co，Zn)W型六元系铁氧体的核壳光纤，选择锌取代铁氧体，旨在控制低频和宽频率范围内的共振模式的磁序参数，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)，其中计划进行Lorenz-TEM和SMM研究，以根据磁性、铁电和电磁参数对纤维和界面进行成像。(Iii)研究局部机械、电磁和磁激励对单个纳米线和组件的ME效应，以建立ME耦合强度、复合材料的对称性/连接性和场定向组装参数之间的关联，并优化纳米复合材料的形貌，以实现最大的ME响应。(4)对单个纳米复合材料和组件中的场定向组装和ME相互作用进行建模，以便与数据进行比较。总体而言，这项研究不仅增强了对纳米材料中ME效应的基本了解，而且对一系列新的传感器、信号处理和能源设备也很有用。该奖项反映了NSF的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。

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.