Ψ-k workshop on magnetism in complex systems, 16 th – 19 th April 2009, TU WienM. Stöger-Pollach Detection of magnetic properties on the nanometer scale Michael Stöger-Pollach, TU Wien Peter Schattschneider, TU Wien Stefano Rubino, Uppsala Univ. Cécile Hébert, EPF Lausanne

Ψ-k workshop on magnetism in complex systems, 16 th – 19 th April 2009, TU WienM. Stöger-Pollach Line out Introduction XMCD/EMCD Recent results Experimental limits Conclusion Introduction XMCD/EMCD basic equations Recent results Experimental limits Conclusion

Ψ-k workshop on magnetism in complex systems, 16 th – 19 th April 2009, TU WienM. Stöger-Pollach Line out Introduction XMCD/EMCD Recent results Experimental limits Conclusion Introduction

Ψ-k workshop on magnetism in complex systems, 16 th – 19 th April 2009, TU WienM. Stöger-Pollach 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?

Ψ-k workshop on magnetism in complex systems, 16 th – 19 th April 2009, TU WienM. Stöger-Pollach Line out Introduction XMCD/EMCD Recent results Experimental limits Conclusion J. Stöhr, Stanford University LiIO 3

Ψ-k workshop on magnetism in complex systems, 16 th – 19 th April 2009, TU WienM. Stöger-Pollach Line out Introduction XMCD/EMCD Recent results Experimental limits Conclusion Wien2k calculations

Ψ-k workshop on magnetism in complex systems, 16 th – 19 th April 2009, TU WienM. Stöger-Pollach Line out Introduction XMCD/EMCD Recent results Experimental limits Conclusion Information in XMCD © Gisela Schütz, MPI Stuttgart Schattschneider et al Nature 441(2006)486-8

Ψ-k workshop on magnetism in complex systems, 16 th – 19 th April 2009, TU WienM. Stöger-Pollach Line out Introduction XMCD/EMCD Recent results Experimental limits Conclusion X-ray Spectromicroscopy PEEM2 (ALS): at resol. limit nm, 0.45 eV FEGTEM: nm, 0.7 eV X-ray photoemission electron microscopy (XPEEM) for dichroism: J. Stöhr et al. 1998

Ψ-k workshop on magnetism in complex systems, 16 th – 19 th April 2009, TU WienM. Stöger-Pollach Line out Introduction XMCD/EMCD Recent results Experimental limits Conclusion X-ray Spectromicroscopy

Ψ-k workshop on magnetism in complex systems, 16 th – 19 th April 2009, TU WienM. Stöger-Pollach Line out Introduction XMCD/EMCD Recent results Experimental limits Conclusion Transmission Electron Microscopy electron source Sample Diffraction pattern 1 st image Condenser projection lenses Objective lens viewing screen image mode diffraction mode

Ψ-k workshop on magnetism in complex systems, 16 th – 19 th April 2009, TU WienM. Stöger-Pollach Line out Introduction XMCD/EMCD Recent results Experimental limits Conclusion Electron Energy Loss Spectrometry Diffraction pattern Fe Co Ni X-ray absorption

Ψ-k workshop on magnetism in complex systems, 16 th – 19 th April 2009, TU WienM. Stöger-Pollach 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 Line out Introduction XMCD/EMCD Recent results Experimental limits Conclusion

Ψ-k workshop on magnetism in complex systems, 16 th – 19 th April 2009, TU WienM. Stöger-Pollach Line out Introduction XMCD/EMCD Recent results Experimental limits Conclusion XMCD/EMCD (X-ray Magnetic Circular Dichroism) (Energy loss Magnetic Chiral Dichroism) - basic equations: Fe Co Ni XANES: X-ray Absorption Near Edge Structure ELNES: Energy Loss Near Edge Structure

Ψ-k workshop on magnetism in complex systems, 16 th – 19 th April 2009, TU WienM. Stöger-Pollach Line out Introduction XMCD/EMCD Recent results Experimental limits Conclusion Similarities ELNES - XANES Dipole approximation No interference... Electrons: Photons (X-rays): (= fine structure in absorption edges)

Ψ-k workshop on magnetism in complex systems, 16 th – 19 th April 2009, TU WienM. Stöger-Pollach Line out Introduction XMCD/EMCD Recent results Experimental limits Conclusion The Mixed Dynamic Form Factor (MDFF) Dynamic Form Factor Static Form Factor Special cases:

Ψ-k workshop on magnetism in complex systems, 16 th – 19 th April 2009, TU WienM. Stöger-Pollach Line out Introduction XMCD/EMCD Recent results Experimental limits Conclusion Mach-Zehnder setup Mixed Dynamic Form Factor angular EELS profiles Inelastic interference

Ψ-k workshop on magnetism in complex systems, 16 th – 19 th April 2009, TU WienM. Stöger-Pollach Line out Introduction XMCD/EMCD Recent results Experimental limits Conclusion XMCD/EMCD Polarization vector in XANES Momentum transfer q in ELNES Matrix elements of DFF in dipole approximation:

Ψ-k workshop on magnetism in complex systems, 16 th – 19 th April 2009, TU WienM. Stöger-Pollach Line out Introduction XMCD/EMCD Recent results Experimental limits Conclusion XMCD/EMCD ELNES: q vectors in diffraction plane EELS at Thales circle XANES: polarization vectors Phase shift π/2 reverse magnetisation measure difference spectra Laue circle centre at (200) reverse current in lens difference spectra prop. to MDFF (200) (000) e2e2 e1e1 C. Hébert & P. Schattschneider, Ultramicroscopy 96 (2003) 463

Ψ-k workshop on magnetism in complex systems, 16 th – 19 th April 2009, TU WienM. Stöger-Pollach Line out Introduction XMCD/EMCD Recent results Experimental limits Conclusion Recent results

Ψ-k workshop on magnetism in complex systems, 16 th – 19 th April 2009, TU WienM. Stöger-Pollach Line out Introduction XMCD/EMCD Recent results Experimental limits Conclusion Detector shift method qq‘ q + _ Schattschneider et al Nature 441(2006)486-8

Ψ-k workshop on magnetism in complex systems, 16 th – 19 th April 2009, TU WienM. Stöger-Pollach Line out Introduction XMCD/EMCD Recent results Experimental limits Conclusion Magnetic phase transition

Ψ-k workshop on magnetism in complex systems, 16 th – 19 th April 2009, TU WienM. Stöger-Pollach Line out Introduction XMCD/EMCD Recent results Experimental limits Conclusion E-q mode of spectrometer energy axis of spectrometer Ni L 3,2 edge, focused spot

Ψ-k workshop on magnetism in complex systems, 16 th – 19 th April 2009, TU WienM. Stöger-Pollach Line out Introduction XMCD/EMCD Recent results Experimental limits Conclusion E-q mode of spectrometer Co L 3,2 edge, focused spot P. Schattschneider, et al

Ψ-k workshop on magnetism in complex systems, 16 th – 19 th April 2009, TU WienM. Stöger-Pollach Scanning mode (STEM) Line out Introduction XMCD/EMCD Recent results Experimental limits Conclusion a) Fe L 3 signal in diffraction plane b) dichroic signal

Ψ-k workshop on magnetism in complex systems, 16 th – 19 th April 2009, TU WienM. Stöger-Pollach Line out Introduction XMCD/EMCD Recent results Experimental limits Conclusion Scanning mode (STEM) minus plus Au FeAuFe 31 nm Fe L 3,2 edge

Ψ-k workshop on magnetism in complex systems, 16 th – 19 th April 2009, TU WienM. Stöger-Pollach Line out Introduction XMCD/EMCD Recent results Experimental limits Conclusion Scanning mode (STEM) P. Schattschneider, et al

Ψ-k workshop on magnetism in complex systems, 16 th – 19 th April 2009, TU WienM. Stöger-Pollach Line out Introduction XMCD/EMCD Recent results Experimental limits Conclusion Scanning mode (STEM) + E-q mode of spectrometer thickness of Fe (nm): Au Fe

Ψ-k workshop on magnetism in complex systems, 16 th – 19 th April 2009, TU WienM. Stöger-Pollach Line out Introduction XMCD/EMCD Recent results Experimental limits Conclusion Scanning mode (STEM) + E-q mode of spectrometer Fe signal dichroic signal

Ψ-k workshop on magnetism in complex systems, 16 th – 19 th April 2009, TU WienM. Stöger-Pollach Line out Introduction XMCD/EMCD Recent results Experimental limits Conclusion Experimental limits Sample thickness Intensity (SNR) Drift of specimen during measurements + -

Ψ-k workshop on magnetism in complex systems, 16 th – 19 th April 2009, TU WienM. Stöger-Pollach Conclusion Line out Introduction XMCD/EMCD Recent results Experimental limits 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

Ψ-k workshop on magnetism in complex systems, 16 th – 19 th April 2009, TU WienM. Stöger-Pollach Thank you for your interest