The group owns a Kerr microscope, which uses the magneto optical Kerr effect to visualize the magnetization and spin structures in thin films and mesoscopic elements including magnetic domains, labyrinth patterns and skyrmions down to sub-micrometer scale resolution. The Kerr effect describes the rotation of the polarization of light when reflected from a magnetized surface. Using a polarizer, the rotated part of the light can be detected and thus one can visualize the magnetization of the surface.
Fig. 1: Kerr effect: The incoming linear polarized light is reflected from the surface and its polarization is rotated by the Kerr angle based on the magnetization of the material’s surface.
An array of LEDs connected to the microscope enables measurements in polar, longitudinal, and transverse mode for the visualization of different magnetization directions. One can observe the samples directly or by a camera, which is connected to the PC. The software processes the images, for example by performing background subtraction to improve the contrast of the magnetization of the samples, thus allowing for real-time observation of changes in the magnetic state. To switch the magnetization, coils, controlled by the software, produce the necessary magnetic fields. Measurements with applied electric currents and at variable temperature are also possible.
The setup is easy to use and quick to set up, making it an efficient tool for a quick hysteresis measurement to characterize a sample or to visualize magnetic structures and their time dependent changes. The camera allows measurements up to 40 frames per second, so even rapid changes of magnetic structures can be resolved. Additionally, a helium flow cryostat allows for measurements near liquid helium temperature, broadening the range of possible measurements.
Fig.2: Kerr microscope with in-plane magnet setup
Fig. 3: Typical Kerr microscopy pictures. Left: skyrmion lattice. The dark dots are skyrmions; magnetic whirls, on an opposed magnetized background. Right: magnetic labyrinth patterns
J. ZÁZVORKA et al., Thermal skyrmion diffusion used in a reshuffler device, Nature Nanotechnology 14(7), 658 (2019)
J. ZÁZVORKA et al., Skyrmion Lattice Phases in Thin Film Multilayer, Advanced Functional Materials 2004037 (2020)
N. KERBER et al., Anisotropic skyrmion diffusion controlled by field-induced symmetry breaking, arXiv:2004.07976 [cond-mat.mtrl-sci] (2020)