Unconventional Kerr Magnetometry - Rudolf Schäfer

Unconventional Kerr microscopy Prof. Rudolf Schäfer Leibniz Institute for Solid State and Materials Research (IFW) Dresden, Helmholtzstrasse 20, D-01069 Dresden, Germany In conventional Kerr- and Faraday microscopy the sample is illuminated with plane-polarised light and a magnetic domain contrast is generated by an analyser making use of the Kerr- or Faraday rotation. In this presentation we review possibilities of analyser-free magneto-optical microscopy based on magnetisation-dependent intensity modulations of the light: (i) The transverse Kerr effect can be applied for in-plane magnetised material, demonstrated for an FeSi sheet. (ii) Illuminating the same sample with circularly polarised light leads to a domain contrast with a different symmetry as the conventional Kerr contrast. (iii) Circular polarisation can also be used for perpendicularly magnetised material, demonstrated for a garnet film and an ultrathin CoFeB film. (iv) Plane-polarised light at a specific angle can be employed for both, in-plane and perpendicular media. (v) Perpendicular light incidence leads to a domain contrast on in-plane materials that is quadratic in the magnetisation and to a domain boundary contrast. (vi) Domain contrast can even be obtained without polariser. In cases (ii) and (iii), the contrast is generated by MCD (Magnetic Circular Dichroism, i.e. by the differential absorption of left and right circularly polarised light, induced by magnetization components along the direction of light propagation) while MLD (Magnetic Linear Dichroism, i.e. by the differential absorption of linearly polarised light, induced by magnetisation components transverse to the propagation direction) is responsible for the contrast in case (v). The domain boundary contrast is due to the magneto-optical gradient effect in metallic samples. A domain boundary contrast can also arise due to interference of phase-shifted magneto-optical amplitudes. All reported contrasts can be applied directly for domain imaging. In any case they need to be considered also in conventional magneto-optical Kerr microscopy and MOKE magnetometry as they can be superimposed on any regular Kerr signal. Ref.: R. Schäfer, P.M. Oppeneer, A. Ognev, A. Samardak, and I.V. Soldatov: Analyser-free, intensity-based wide-field magneto-optical microscopy. Appl. Phys. Rev. 8, 031402 (2021) —————— Rudolf Schaefer studied Materials Science and received the Ph.D. in Engineering at Erlangen-University in 1990. After Postdoc stays at IBM Research in Yorktown Heights and Forschungszentrum Juelich he moved to IFW Dresden in 1993, where currently he heads the Institute for Integrative Nanosciences. In 2011, R. Schaefer was appointed adjunct professor for Magnetic Materials at TU Dresden. He became Distinguished Lecturer of the IEEE Magnetics Society in 2013 and currently chairs the Conference Executive Committee of the Society. His interest areas span magnetic materials with focus on magnetic microstructures. He has published more than 200 technical articles in peer-reviewed journals, including book chapters and 2 monographs.