Exploring new functionalities of magnetic materials utilizing nanoplasmonics and multiferroics

该提案的目的是利用纳米等离子体激元和多铁性来探索磁性材料的新功能。特别是，我们有兴趣开发新的方法来控制磁性光学或电气。 在研究的第一部分，我们将研究光与磁之间的相互作用，这在基础科学和技术应用方面至关重要。一个具体的目标是磁的超快光控制。然而，光与磁性介质的相互作用强度非常弱，这种弱相互作用一直是光学探测或控制磁性的主要挑战。为了克服这个缺点，我们将利用磁等离子体激元，它结合了磁性和等离子体功能。在我们以前的研究中，我们观察到在铁磁薄膜中掺入贵金属纳米颗粒显著增强了磁光（MO）效应。我们将对等离子体共振对分子轨道效应的影响进行系统的研究，并对分子轨道活性增强的潜在机制有更好的理解。我们也将研究光激发高能电子所引发的超快磁性。需要回答的问题是：我们能否通过局域表面等离子体共振增强超热电子的光学产生？如果是这样，我们如何有效地操纵热电子诱导的超快磁过程？另一个项目是利用超快光激发产生大波数自旋波。已知自旋波数由泵浦光的空间强度分布决定。我们将能够通过使用近场光学将泵浦光斑尺寸减小到纳米级。更高的自旋波数也可以通过使用局部表面等离子体共振来产生，其中空间强度分布由纳米颗粒的几何形状决定。 研究的第二部分是探索利用磁电多铁性材料的电场控制磁性的机会，这使得磁性和铁电有序之间的耦合成为可能。然而，室温多铁性是非常罕见的，与BiFeO3（BFO）是一个例外。它的缺点是它的磁矩很弱。最近，人们发现双钙钛矿材料Bi2FeCrO6（BFCO）具有与BFO类似的铁电性，并具有强磁矩的附加益处。我们的主要目标是回答这个问题是否BFCO可以提供一个新的途径电场切换的磁性。我们也将探讨电场触发的磁化动力学在门控BFCO薄膜。考虑到由多铁性材料实现的磁场控制具有彻底改变当今电子技术的潜力，所提出的研究成果将具有重大意义。

The purpose of this proposal is to explore new functionalities of magnetic materials utilizing nanoplasmonics and multiferroics. In particular, we are interested in developing new ways to control magnetism optically or electrically. In the first part of the research, we will investigate the interaction between light and magnetism, which is of utmost importance in terms of fundamental science and technological applications. A specific goal is the ultrafast light control of magnetism. The strength of the interaction of light with a magnetic medium, however, is very weak, and this weak interaction has been the main challenge in optically probing or controlling magnetism. In order to overcome this drawback, we will exploit magneto-plasmonics, which combines magnetic and plasmonic functionalities. In our previous studies, we observed that the incorporation of noble-metal nanoparticles in ferromagnetic films significantly enhances magneto-optical (MO) effect. We will conduct systematic studies on the influence of plasmon resonance on MO effect, and develop a better understanding of the underlying mechanism of the enhanced MO activities. We will also study the ultrafast magnetism triggered by optically excited high energy electrons. The questions to be answered are: can we enhance the optical generation of hot electrons via localized surface plasmon resonance? If so, how effectively can we manipulate the hot-electron induced ultrafast magnetic process? Another project is to generate large wavenumber spin waves using ultrafast optical excitation. It is known that the spin wavenumber is determined by the spatial intensity distribution of the pumping light. We will be able to reduce the pump spot size to the nanoscale by using near-field optics. Higher spin wavenumbers can also be generated by using the localized surface plasmon resonance, in which the spatial intensity distribution is determined by the geometries of the nanoparticles. The second part of the research is to explore the opportunity of electric-field control of magnetism utilizing magnetoelectric multiferroics, which enables the coupling between magnetic and ferroelectric orders. However, room temperature multiferroics are very rare, with BiFeO3 (BFO) being an exception. Its drawback is that it has a very weak magnetic moment. Recently, it was found that a double perovskite material Bi2FeCrO6 (BFCO) has ferroelectricity similar to BFO with the added benefit of a strong magnetic moment. Our main goal is to answer the question whether BFCO can provide a new avenue for electric-field switching of magnetism. We will also investigate the electric-field triggered magnetization dynamics in gated BFCO thin films. Considering that the electric-field control of magnetism enabled by multiferroics has the potential to revolutionize today's electronics technology, the outcome of the proposed research will be significant.