Invited Paper MI-ThM9
Magnetic Soft X-ray Microscopy: Challenges and Opportunities to Image Fast Spin Dynamics on the Nanoscale

Thursday, November 12, 2009, 10:40 am, Room C1

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 to provide a fundamental understanding of the physical processes involved.

Magnetic soft X-ray microscopy is a powerful analytical technique since it combines 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 <15nm [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.

I will review recent achievements 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. The unique features of soft X-ray microscopy and the current developments with regard to improved X-ray optics and high brilliant fsec X-ray sources seems to make this technique a strong candidate to meet this challenge.

Collaboration with M.-Y. Im, B.L. Mesler, W.Chao (CXRO), G. Meier, L. Bocklage, M. Bolte, R.Eiselt, B. Krueger, D. Pfannkuche, U. Merkt (U Hamburg), S. Kasai, K. Yamada, K. Kobayashi, T. Ono (U Kyoto), Y. Nakatani (U Chofu), H. Kohno (U Osaka), A. Thiaville (U Paris-Sud), D.H. Kim (Chungbuk U) and S.-C. Shin (KAIST) is greatly appreciated. Supported by the Director, Office of Science, Office of Basic Energy Sciences, Materials Sciences and Engineering Division, of the U.S. Department of Energy.

References

[1] D.-H. Kim, et al., J. Appl. Phys. 99, 08H303, (2006)

[2] M.-Y. Im, et al, Advanced Materials 20 1750 (2008)

[3] G. Meier et al., Phys. Rev. Lett. 98, 187202 (2007)

[4] M.-Y. Im, et al., Phys Rev Lett 102 147204 (2009)

[5] L. Bocklage, et al., Phys Rev B 78 180405(R) (2008)

[6] S. Kasai, et al., Phys Rev Lett 101, 237203 (2008)