Doped BiFeO3 Nanoparticles

几十年来，磁电材料一直吸引着研究人员。本征多铁性材料通常在远低于室温的温度下表现出这种耦合。到目前为止，已知的室温多铁质材料很少，它们在室温下都表现出反铁磁秩序，从而产生几乎消失的有效磁电耦合。最有趣的候选者是铋铁氧体BiFeO3，因为磁矩本身不是反平行的，而是在许多单元胞中产生摆线秩序。总的来说，这些磁矩被取消了，但希望是打破或修改这个顺序，并为应用建立一个合理大小的有限磁矩。到目前为止，大量掺杂和薄膜形成是试图调整这些特性的主要途径。在掺杂纳米颗粒中，预计巨大表面积的附加影响将改变摆线秩序并增强磁电耦合。关于二次磁性粒子的共掺杂和纳米粒子表面修饰的效果，目前所知不多。这个建议涉及到制造和研究这些粒子。在这个最初的提议中，将主要讨论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-凝胶或有机溶胶方法的化学合成。我们一直在生产多种不同的陶瓷纳米颗粒，包括纳米级的核壳和覆盆子结构。制造名义上纯净的BiFeO3非常成功。这些技术现在打算应用于共掺杂BiFeO3。表征包括经典技术，SQUID磁强计，阻抗分析（也局部）和扫描探针显微镜技术。为了改变颗粒尺寸，不仅要使用化学方法，而且要使用激光合成和加工方法，产生的颗粒尺寸大多比化学方法小。因此，整个范围从20到1000纳米可以被覆盖。和大家一样，我们希望增强粒子的有效磁矩和磁电耦合。我们提供了一个很有前途的新方法。

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.