Detection of magnetic properties on the nanometer scale

1. Detection of magnetic properties on thenanometer scale Michael Stöger-Pollach, TU Wien Peter Schattschneider, TU Wien Stefano Rubino, Uppsala Univ. Cécile Hébert, EPF Lausanne

2. Line out Introduction XMCD/EMCD Recent results Experimental limits Conclusion Line out Experimental limits Introduction XMCD/EMCDbasic equations Conclusion Recent results

3. Line out Introduction XMCD/EMCD Recent results Experimental limits Conclusion Introduction

4. Line out Introduction XMCD/EMCD Recent results Experimental limits Conclusion Definition • Dichroism := dependence of X-ray absorption coefficient on the polarization of the photon • linear dichroism: linearly polarized photon measures anisotropy • circular dichroism: circularly polarized photon measures chirality (XMCD) Circular dichroism in the TEM? XMCD: polarization vector of photon rotates  do we need spin polarized probe electrons?

5. Line out Introduction XMCD/EMCD Recent results Experimental limits Conclusion LiIO3 J. Stöhr, Stanford University

6. Line out Introduction XMCD/EMCD Recent results Experimental limits Conclusion Schattschneider et alNature441(2006)486-8 Information in XMCD © Gisela Schütz, MPI Stuttgart

7. Line out Introduction XMCD/EMCD Recent results Experimental limits Conclusion X-ray Spectromicroscopy X-ray photoemission electron microscopy (XPEEM) for dichroism: J. Stöhr et al. 1998 PEEM2 (ALS): at resol. limit 106 photons/s @ 20 nm, 0.45 eV FEGTEM: 3.109 electrons/s @ 0.7 nm, 0.7 eV

8. Line out Introduction XMCD/EMCD Recent results Experimental limits Conclusion X-ray Spectromicroscopy

9. Line out Introduction XMCD/EMCD Recent results Experimental limits Conclusion Transmission Electron Microscopy electron source Condenser Sample Diffraction pattern Objective lens 1st image projection lenses viewing screen diffraction mode image mode

10. Line out Introduction XMCD/EMCD Recent results Experimental limits Conclusion Ni Fe Co X-ray absorption Electron Energy LossSpectrometry Diffraction pattern

11. Line out Introduction XMCD/EMCD Recent results Experimental limits Conclusion XMCD: synchrotron Availability: 60 world wide Price: > 900 M$ (Brookhaven NSLS II) EMCD: TEM and EELS Availability: many, many, many world wide Price: ~ 2 M$(TECNAI F20) Spatial resolution: ~20 nm (XPEEM) Spatial resolution: <1 nm

12. Line out Introduction XMCD/EMCD Recent results Experimental limits Conclusion XANES:X-ray Absorption Near Edge Structure ELNES:Energy Loss Near Edge Structure Ni Fe Co XMCD/EMCD(X-ray Magnetic Circular Dichroism)(Energy loss Magnetic Chiral Dichroism)- basic equations:

13. Line out Introduction XMCD/EMCD Recent results Experimental limits Conclusion Similarities ELNES - XANES (= fine structure in absorption edges) No interference... Dipole approximation Electrons: Photons(X-rays):

14. Line out Introduction XMCD/EMCD Recent results Experimental limits Conclusion Special cases: Dynamic Form Factor Static Form Factor The Mixed Dynamic Form Factor (MDFF)

15. Line out Introduction XMCD/EMCD Recent results Experimental limits Conclusion angular EELS profiles Mach-Zehnder setup Mixed Dynamic Form Factor Inelastic interference

16. Line out Introduction XMCD/EMCD Recent results Experimental limits Conclusion Polarization vector in XANESMomentum transfer q in ELNES Matrix elements of DFF in dipole approximation: XMCD/EMCD

17. Line out Introduction XMCD/EMCD Recent results Experimental limits Conclusion e1 e2 (200) (000) XMCD/EMCD XANES: polarization vectors ELNES: q vectors in diffraction plane EELS at Thales circle Phase shift π/2 reverse magnetisation measure difference spectra Laue circle centre at (200) reverse current in lens difference spectra prop. to MDFF C. Hébert & P. Schattschneider, Ultramicroscopy96 (2003) 463

18. Line out Introduction XMCD/EMCD Recent results Experimental limits Conclusion Recent results

19. Line out Introduction XMCD/EMCD Recent results Experimental limits Conclusion q q‘ q q‘ Detector shift method + _ Schattschneider et al Nature 441(2006)486-8

20. Line out Introduction XMCD/EMCD Recent results Experimental limits Conclusion Magnetic phase transition

21. Line out Introduction XMCD/EMCD Recent results Experimental limits Conclusion energy axis of spectrometer E-q mode of spectrometer Ni L3,2 edge, focused spot

22. Line out Introduction XMCD/EMCD Recent results Experimental limits Conclusion P. Schattschneider, et al E-q mode of spectrometer Co L3,2 edge, focused spot

23. Line out Introduction XMCD/EMCD Recent results Experimental limits Conclusion Scanning mode (STEM) a) Fe L3 signal in diffraction planeb) dichroic signal

24. Line out Introduction XMCD/EMCD Recent results Experimental limits Conclusion Scanning mode (STEM) 31 nm 10 6 3 Au Fe Au Fe minus Fe L3,2 edge plus

25. Line out Introduction XMCD/EMCD Recent results Experimental limits Conclusion P. Schattschneider, et al Scanning mode (STEM)

26. Line out Introduction XMCD/EMCD Recent results Experimental limits Conclusion Scanning mode (STEM) + E-q mode of spectrometer Au Fe thickness of Fe (nm): 1 1 2 3 15

27. Line out Introduction XMCD/EMCD Recent results Experimental limits Conclusion Fe signal dichroic signal Scanning mode (STEM) + E-q mode of spectrometer

28. Line out Introduction XMCD/EMCD Recent results Experimental limits Conclusion + - Experimental limits Sample thickness Intensity (SNR) Drift of specimen during measurements

29. Line out Introduction XMCD/EMCD Recent results Experimental limits Conclusion Conclusion • with EMCD we are able to detect magnetic properties on nm-level • Mapping of magnetic properties was not achieved within EMCD until now • Stabilibty problems and little brigtness need to be improved

30. Thank you foryour interest