Magneto-Optic Analysis of Magnetic Microstructures

R. Schaefer
Leibniz Institute for Solid State and Materials Research (IFW) Dresden, Germany

The characterization of magnetic materials in research and development usually relies on the measurement of hysteresis curves as the most basic characterization means. Microscopically, the shape of such loops is determined by the magnetic microstructure of the material. The knowledge of magnetic domains and their substructures (domain walls, swirls etc.) is therefore essential for the interpretation of magnetization curves. Magnetic microstructures, on the other hand, may be more or less complex and their analysis challenging. Micromagnetic theory, both analytical as well as numerical, is limited to few suitable cases for which the micromagnetic equations can be linearized or to small structures in the micrometer regime at best, respectively. In most practical cases there is rather no way around imaging and using arguments from domain theory for the interpretation of the images.

Magneto-optical microscopy, in particular Kerr microscopy, is just one among many techniques to image domains and processes, and it may be considered a „classical“ method (compared to „modern“ magnetic microscopy based, e.g, on circular X-ray dichroism or spin-polarized tunneling). Nevertheless, Kerr microscopy is the most flexible and versatile technique and due to substantial technical progress in recent time, magneto-optical domain imaging becomes very powerful again.

In this presentation, a review will be given on the possibilities and recent developments of magnetic domain imaging by wide-field magneto-optical microscopy. Besides some basics, this includes depth-sensitive and time-resolved domain imaging, a mathematical deconvolution method to enhance the lateral resolution, and on the other hand an overview imaging tool to maximize the field of view. Novel light-emitting diode (LED) lamps allow for contrast separation and -enhancement, vector magnetometry and in-situ quantitative Kerr microscopy of complete magnetization processes, as will be demonstrated on magnetic film and bulk materials.