Doped BiFeO3 Nanoparticles

几十年来，磁电材料一直吸引着研究人员的兴趣。本征多铁体通常在远低于室温的温度下表现出这样的耦合。到目前为止，只有少数几种室温下的多铁性材料是已知的，它们在室温下都表现出反铁磁有序，产生的有效磁电耦合几乎为零。最有趣的候选者是铋铁氧体BiFeO_3，因为磁矩本身并不是反平行的，而是在许多单元上产生摆线有序。总体而言，这些磁矩被抵消了，但希望打破或修改这种秩序，并为应用建立一个合理量级的有限磁矩。到目前为止，块体掺杂和薄膜形成一直是试图定制这些特性的主要途径。在掺杂纳米粒子中，巨大表面积的附加影响有望改变摆线有序，并增强磁电耦合。关于二次磁性粒子的共掺杂和纳米粒子表面修饰的影响，人们知之甚少。这项提议涉及到制造和研究这些粒子。在这个最初的提案中，将讨论主要掺杂和共掺杂的变体。该项目的主要部分是基于内部开发的类似于溶胶凝胶法或有机溶胶法的化学合成。我们一直在生产各种不同的陶瓷纳米颗粒，包括纳米级的核、壳和覆盆子结构。制备名义上纯净的BiFeO_3已经非常成功。这些技术现在打算应用于共掺杂BiFeO_3。表征包括经典技术、SQUID磁测量、阻抗分析(也包括局部)和扫描探针显微镜技术。为了改变颗粒大小，不仅要使用化学路线，而且要使用激光合成和加工路线，以产生比化学技术更小的颗粒尺寸。因此，可以覆盖从20纳米到1000纳米的整个范围。像其他人一样，我们希望增强粒子的有效磁矩和磁电耦合。我们提供了一种很有前途的新方法。

Magnetoelectric materials have been intriguing researchers for several decades. Intrinsic multiferroics exhibit such coupling usually at temperatures well below room temperature. So far, only a few room temperature multiferroics are known, all exhibiting an antiferromagnetic order at room temperature which yields practically vanishing effective magnetoelectric coupling. The most interesting candidate is bismuth ferrite, BiFeO3, because the magnetic moments are not antiparallel per se, but generate cycloidal order across many unit cells. Overall these moments cancel, but hope is to break up or modify this order and establish a finite magnetic moment of reasonable magnitude for applications. So far, bulk doping and thin film formation have been the major routes trying to tailor these properties. In doped nanoparticles the additional influence of the huge surface area is anticipated to modify the cycloidal order as well as to enhance magnetoelectric coupling. Not much is known on the effect of co-doping and nanoparticle surface decoration with secondary magnetic particles. This proposal deals with making and investigating these particles. In this initial proposal mostly doped and co-doped variants will be addressed. The major part of the project is focused on chemical synthesis based on an in house developed route similar to the sol-gel or organosol methods. We have been producing a multitude of different ceramic nanoparticles including core shell and raspberry structures at the nanoscale. Making of nominally pure BiFeO3 has been very successful. These techniques are now intended to be applied to co-doped BiFeO3. Characterization comprises classical techniques, SQUID magnetometry, impedance analysis (also locally), and scanning probe microscopy techniques. In order to vary particle size, not only the chemical route is intended for use, but also laser synthesis and processing routes yielding mostly smaller particle sizes than the chemical techniques. Thus the whole range from 20 to 1000 nanometers can be covered. Like everyone else, we hope to enhance the effective magnetic moment of the particles and magnetoelectric coupling. We offer a promising new approach.