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

Detection of magnetic properties on

thenanometer 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, 16th – 19th April 2009, TU Wien M. Stöger-Pollach

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Introduction

XMCD/EMCD

Recent results

Experimental limits

Conclusion Introduction

XMCD/EMCDbasic equations

Recent results

Experimental limits

Conclusion

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

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Introduction

XMCD/EMCD

Recent results

Experimental limits

Conclusion

Introduction

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

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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, 16th – 19th April 2009, TU Wien M. Stöger-Pollach

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Introduction

XMCD/EMCD

Recent results

Experimental limits

Conclusion

J. Stöhr, Stanford University

LiIO3

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

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Introduction

XMCD/EMCD

Recent results

Experimental limits

Conclusion

Information in XMCD© Gisela Schütz,

MPI Stuttgart

Schattschneider et alNature 441(2006)486-8

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

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Introduction

XMCD/EMCD

Recent results

Experimental limits

Conclusion

X-ray Spectromicroscopy

PEEM2 (ALS): at resol. limit 106 photons/s @ 20 nm, 0.45 eV

FEGTEM: 3.109 electrons/s @ 0.7 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, 16th – 19th April 2009, TU Wien M. Stöger-Pollach

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Introduction

XMCD/EMCD

Recent results

Experimental limits

Conclusion

X-ray Spectromicroscopy

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

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Introduction

XMCD/EMCD

Recent results

Experimental limits

Conclusion

Transmission Electron Microscopy

electron sourceelectron source

SampleSample

Diffraction pattern

Diffraction pattern

1st image1st image

CondenserCondenser

projection lensesprojection lenses

Objective lensObjective lens

viewing screenviewing screen

image mode diffraction mode

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

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Introduction

XMCD/EMCD

Recent results

Experimental limits

Conclusion

Electron Energy Loss

Spectrometry

Diffraction patternDiffraction pattern

Fe

Co

Ni

X-ray absorption

Ψ-k workshop on magnetism in complex systems, 16th – 19th April 2009, TU Wien M. 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

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Introduction

XMCD/EMCD

Recent results

Experimental limits

Conclusion

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

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Introduction

XMCD/EMCD

Recent results

Experimental limits

Conclusion

XMCD/EMCD(X-ray Magnetic Circular Dichroism)

(Energy loss Magnetic Chiral Dichroism)

- basic equations:Fe

Co

NiXANES: X-ray Absorption Near Edge Structure

ELNES: Energy Loss Near Edge Structure

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

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Introduction

XMCD/EMCD

Recent results

Experimental limits

Conclusion2 2

,* *2 4 2 20

( , ) ( , )4(1 ) f j j lj j j l

ELNES j j li j j l

k DFF E MDFF Ec c c c

E a k q q q

q q q

2

,

2 ( )XANES i fi f

h i f E E E e R

Similarities ELNES - XANES

Dipole approximation

2

,

ˆ( , ) ( )i fi f

DFF E i f E E E q qR

2

,

( , ) ( )i fi f

iDFF E i f E E Ee Rqq

No interference...

Electrons:

Photons(X-rays):

(= fine structure in absorption edges)

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

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Introduction

XMCD/EMCD

Recent results

Experimental limits

Conclusion

The Mixed Dynamic Form Factor (MDFF)

Dynamic Form Factor

Static Form Factor 2,0, FMDFF qq

,, DFFEMDFF qq

Special cases:

,

'( , ', ) ( )i fi f

i iMDFF E i f f i E E Ee e R Rq qq q

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

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Introduction

XMCD/EMCD

Recent results

Experimental limits

Conclusion

Mach-Zehnder setup

2 2 21 2,

122 4 2 210 1 2

( , ) ( , )4 (1 ) f j

ji j

k DFF E MDFF EC

E a k q q q

q q q

Mixed Dynamic Form Factor

direct(Lorentzians)

interference (Kikuchi band)

angular EELS profiles

Inelastic interference

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

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Introduction

XMCD/EMCD

Recent results

Experimental limits

Conclusion

XMCD/EMCDPolarization vector in XANES Momentum transfer q in ELNES

1 2e i e 'q i qMatrix elements of DFF in dipole approximation:

2 22

, , ,

, ,

ˆ ˆ ˆ( ') '

ˆ ˆ ˆ ˆ' '

i f i f i f

i f i f

i i R f i R f i R f

i i R f f R i i R f f R i

q q q q

q q q q

( , ', )MDFF Eq q( ', , )MDFF Eq q

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

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Introduction

XMCD/EMCD

Recent results

Experimental limits

Conclusion

XMCD/EMCDELNES:

q vectors in diffraction planeEELS 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)

e2e1

C. Hébert & P. Schattschneider, Ultramicroscopy 96 (2003) 463

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

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Introduction

XMCD/EMCD

Recent results

Experimental limits

Conclusion

Recent results

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

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Introduction

XMCD/EMCD

Recent results

Experimental limits

Conclusion

Detector shift method

q q‘

q q‘

+

_

Schattschneider et al Nature 441(2006)486-8

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

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Introduction

XMCD/EMCD

Recent results

Experimental limits

Conclusion

Magnetic phase transition

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

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Introduction

XMCD/EMCD

Recent results

Experimental limits

Conclusion

E-q mode of spectrometer

energy axis of spectrometer

Ni L3,2 edge, focused spot

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

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Introduction

XMCD/EMCD

Recent results

Experimental limits

Conclusion

E-q mode of spectrometerCo L3,2 edge, focused spot

P. Schattschneider, et al

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

Scanning mode (STEM)Line out

Introduction

XMCD/EMCD

Recent results

Experimental limits

Conclusion

a) Fe L3 signal in diffraction planeb) dichroic signal

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

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Introduction

XMCD/EMCD

Recent results

Experimental limits

Conclusion

Scanning mode (STEM)

minus

plus

Au Fe Au Fe31 nm 10 6 3

Fe L3,2 edge

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

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Introduction

XMCD/EMCD

Recent results

Experimental limits

Conclusion

Scanning mode (STEM)

P. Schattschneider, et al

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

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Introduction

XMCD/EMCD

Recent results

Experimental limits

Conclusion

Scanning mode (STEM) +

E-q mode of spectrometerth

ickn

ess

of F

e (n

m):

1

1

2

3

15

Au

F

e

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

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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, 16th – 19th April 2009, TU Wien M. Stöger-Pollach

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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, 16th – 19th April 2009, TU Wien M. Stöger-Pollach

ConclusionLine 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, 16th – 19th April 2009, TU Wien M. Stöger-Pollach

Thank you foryour interest