Soft X-Ray Microscopy: Imaging Magnetism at Small Sizes

The manipulation of spins on the nanoscale is of both fundamental and technological interest. In spin based electronics the observation that spin currents can exert a torque onto local spin configurations which can e.g. push a domain wall has stimulated significant research activities in order to provide a fundamental understanding of the physical processes involved. Magnetic soft X-ray microscopy is a unique analytical technique combining X-ray magnetic circular dichroism (X-MCD) as element specific magnetic contrast mechanism with high spatial and temporal resolution. Fresnel zone plates used as X-ray optical elements provide a spatial resolution down to currently $<$12nm [1] thus approaching fundamental magnetic length scales such as the grain size [2] and magnetic exchange lengths. Images can be recorded in external magnetic fields giving access to study magnetization reversal phenomena on the nanoscale and its stochastic character [3] with elemental sensitivity [4]. Utilizing the inherent time structure of current synchrotron sources fast magnetization dynamics with 70ps time resolution, limited by the lengths of the electron bunches, can be performed with a stroboscopic pump-probe scheme. In this talk I will review recent achievements with magnetic soft X-ray microscopy with focus on current induced wall [5] and vortex dynamics in ferromagnetic elements [6]. Future magnetic microscopies are faced with the challenge to provide both spatial resolution in the nanometer regime, a time resolution on a ps to fs scale and elemental specificity to be able to study novel multicomponent and multifunctional magnetic nanostructures and their ultrafast spin dynamics.\\[4pt] References\\[0pt] [1] W. Chao, et al., Optics Express 17(20) 17669 (2009) \\[0pt] [2] M.-Y. Im, et al, Advanced Materials 20 1750 (2008) \\[0pt] [3] M.-Y. Im, et al., Phys Rev Lett 102 147204 (2009) \\[0pt] [4] M.-Y. Im, et al., Appl Phys Lett 95 182504 (2009) \\[0pt] [5] L. Bocklage, et al., Phys Rev B 78 180405(R) (2008) \\[0pt] [6] S. Kasai, et al., Phys Rev Lett 101, 237203 (2008)