Magneto-optical imaging of nanomagnetic structures

近年来，利用材料的磁性进行电子学（自旋电子学）和数据存储的研究取得了巨大的增长。在这两个领域，自旋电子学和磁存储，尺寸和操作速度定义了设备的属性。当磁性元件的尺寸减小到几百纳米以下时，另一个质的变化发生了，因为磁体只能维持单个畴。这对不再依赖于畴壁运动的动态特性具有严重后果。直到今天，单畴水平上的磁化强度变化发生的时间尺度还不清楚。因此，必须发展测量这些基本和技术相关的量的能力，这些量是纳米级磁性器件速度的最终固有极限。我们将研究具有高时间和空间分辨率的纳米级磁性结构的磁化动力学，作为对（纳米）磁性应用产生重大影响的研究领域。超快光学方法，如磁光克尔光谱将用于提供所需的时间分辨率，以解决单畴粒子的磁化方向的变化。基于具有近场扫描显微镜功能的集成超快光谱系统，将建立用于单个单畴（纳米）磁性结构的磁化动力学的磁光测量装置。随后，将对不同尺寸和形状的纳米磁性结构进行测量，以定性和定量地了解磁化反转的时间尺度和机制。此外，还将开发高灵敏度的磁光光谱方法。检测来自单个纳米结构的小磁光反射信号需要极高的灵敏度。因此，磁光克尔效应的腔增强将被研究，以将这种技术扩展到超快单粒子制度。在该项目的过程中，腔增强将首先在较大的样品或纳米磁体阵列中进行研究，然后再应用于单个单畴粒子。 这里提议的工作预计将产生广泛的重大影响。随着磁光学和自旋电子学的发展以及器件尺寸的进一步缩小，测量磁特性的灵敏方法将在确定此类器件的局限性方面发挥重要作用。在该计划的过程中，研究生将在实验研究的两个关键领域，超快光谱学和扫描显微镜进行培训。此外，本科生将积极参与该项目，这项研究的各个方面将被纳入目前正在加州大学圣克鲁斯开发的纳米技术多学科研究生班。

In recent years, research on the use of magnetic properties of materials for electronics (spintronics) and data storage has grown tremendously. In both areas, spintronics and magnetic storage, size and operational speed are defining properties of a device. As the size of a magnetic element is reduced below a few hundred nanometers, another qualitative change occurs as the magnet can only sustain a single domain. This has severe consequences for dynamic properties, which do not depend on domain wall motion anymore. To this day, the time scales over which magnetization changes on the single-domain levels occur are not known. It is therefore essential to develop the capabilities to measure these fundamentally and technologically relevant quantities that present the ultimate intrinsic limit for the speed of nanoscale magnetic devices. We will study the magnetization dynamics of nanoscale magnetic structures with high temporal and spatial resolution as an area of research with large impact on (nano)-magnetic applications. Ultrafast optical methods such as magneto-optical Kerr spectroscopy will be used to provide the time resolution required to resolve changes in the magnetization direction of single-domain particles. Based on an integrated ultrafast spectroscopy system with near-field scanning microscopy capabilities, a setup for the magneto-optical measurement of the magnetization dynamics of single single-domain (nano)-magnetic structures will be built. Subsequently, measurements on nanomagnetic structures of varying sizes and shapes will be carried out to gain a qualitative and quantitative understanding of the magnetization reversal time scales and mechanisms.In addition, highly sensitive magneto-optical spectroscopy methods will be developed. The detection of small magneto-optic reflection signals from individual nanostructures requires exquisite sensitivity. Therefore, cavity enhancement of the magneto-optical Kerr effect will be studied to extend this technique to the ultrafast single-particle regime. In the course of the project, cavity enhancement will first be investigated in larger samples or arrays of nanomagnets before then being applied to individual single-domain particles. The work proposed here is expected to have significant broader impact. As magneto-optics and spintronics evolve and device dimensions shrink further, sensitive methods to measure magnetic properties will play an important role in determining the limitations of such devices. Over the course of the program, graduate students will be trained in two key areas of experimental research, ultrafast spectroscopy and scanning microscopy. In addition, undergraduates will be actively involved in the project and aspects of this research will be incorporated into a multidisciplinary graduate class in nanotechnology currently being developed at UC Santa Cruz.