1.
APR-EMCD
An overview of the paper
Rusz, Ján, Shunsuke Muto, Jakob Spiegelberg, Roman Adam, Kazuyoshi Tatsumi, Daniel E. Bürgler, Peter M. Oppeneer, and Claus M. Schneider.
"Magnetic Measurements with Atomic-plane Resolution."
Nature Communications 7 (2016): 12672. Web.
Thesis for the course of
Microscopies and Nanocharacterization Techniques
Teacher: MARCO ROSSI
Student: RICCARDO DI STEFANO

2.
Circular dichroism (CD) - Differential Absorption of
Circular Dichroism (CD)
Photoelastic Modulator
UV secondary structure of proteins
UV/VIS charge transfer transition
NIR geometric and electronic structure through metal d->d transitions
IR (Vibrational) structural investigation of organic molecules
For the study of

3.
Circular dichroism (CD) - Differential Absorption of
XMCD
Invertible Magnetic
Fields ranging from
0.1T to several Teslas.
X-Rays → High Penetration → sample ≈ μm thick
Soft X-Rays → Low penetration → sample ≈ 100-150nm Thick
CONVENTIONAL SETUP FOR HARD X-RAYS
FOR SOFT X-RAYS

4.
Circular dichroism (CD) - Differential Absorption of
XMCD
Chronologically XMCD was observed in:
• Fe K-edges (Less than 1%)
• Gd, Tb (4%)
• Pt impurities in Fe (Giant signal 22%)
• Fe, Co, Ni (Giant signal, 3d transition metals)
Photon energy (eV)
XAS Spectra
Complex fine structure
The absorption cross-section changes for
changes in the relative orientation between the
magnetization and the helicity of the polarized
photon.
XMCD Occurs for diamagnetic, paramagnetic and
(anti)-ferromagnetic materials.
Δ(𝐸) = 𝐼−
(𝐸) − 𝐼+
(𝐸)
XMCD signal is simply
the difference between
the XAS spectras of left
and right circularly
polarized light:

5.
Circular dichroism (CD) - Differential Absorption of
XMCD (X-Ray MCD)
Main XMCD Limitations
Used techniques and magnetization
dependance of the absorption intensity
Resolution → 10-50 nm spectroscopy
Little signal depth→ XMCD photoemitted microscopy
essentially surface sensitive
θ
M
S
I ∝ cos θ

6.
XMCD & EMCD equivalence
The equivalence can be extended to circular polarization
as we think of a spin polarized photon as a superposition
of two linearly polarized waves dephased by 90° (i). Then
in electronic terms, we can express the wave vector
tranfer as
q ± iq’
|q| = |q’|
q ⊥ q’
with hq, hq’ the momentum transfers in the ionization
impact.
ε formally equivalent to ħq

7.
CONVENTIONAL EMCD
(Electron Magnetic Circular Dichroism)
When an electron beam enters a crystalline beam splitter,
it gets Bragg scattered and decomposes into Bloch waves.
Appropriate boundary conditions (tilt and thickness) allow
us to obtain one or two Bragg scattered beams dephased
by π/2, hence a local chiral electric field arising from
pendellösung oscillations (sinusoidal intensity oscillations
caused by Bloch wave superposition).
INTRINSIC METHOD
Low electron count on Thales
circle + & - spots, aside the
Bragg spots
• 2-beam(or 3) condition, one
transmitted, one Bragg
Scattered.
• The sample acts as a beam
splitter.
• Tilt is a few degrees away
from the Zone Axis
Fe
experiment

8.
STEM-EMCD CONVENTIONAL SETUP
THE EELS DATA CUBE
2 or 3-beam
orientation tilt (few
degrees from the
Zone Axis)

9.
STEM CONVENTIONAL SETUP
Conventional EMCD has potential for
reaching atomic resolution but suffers
low signal-to-noise ratio, not
combining well with limited spectrum
acquisition times in STEM setups,
necessary to prevent sample damage
and drifts.
Astigmatic beams
Electron vortex beams
Low signal
Difficulty in generating
atomic size probes
with desired orbital
angular momentumOther
approaches
Incident vortex
with ring radius
of 0.9 nm and
displaced atoms
Reciprocal space
wave function (WF)
of a beam distorted
by fourfold
astigmatism

10.
2Å
Magnetic measurements with atomic-plane resolution
(APR-EMCD)
Experimental setup
• 200 kV beam
• Fe SAMPLE TILTED TO A 3-BEAM CONDITION
• CONVERGENT ATOMIC SIZE BEAM
Borrowed from
Conventional
EMCD
Borrowed from
Atomic-res EMCD
(Vortex & Astigmatic)
A rectangular Aperture
is placed on the Gatan
Image Filter
10° from the (001)
crystal orientation

11.
Magnetic measurements with atomic-plane resolution
(APR-EMCD)
Experimental setup
Conventional CBED-EMCD
detector placement
(two scans are necessarry for each pixel)
Obtained diffraction pattern in
APR-EMCD
Detector placement in
APR-EMCD

12.
Magnetic measurements with Atomic-Plane Resolution
(APR-EMCD)
THE EELS DATA CUBE
In a single
acquisition we can
obtain:
Thickness/Mass
contrast ADF Image
+
Chiral + & - spectra
(therefore EMCD
spectra)
APR-EMCD does not
require modification of
the STEM microscope
(in this case an aberration
corrected JEM ARM200F
with Gatan Image Filter
Quantum)
The integration can be
related through sum
rules (Theo Thole et al.)
to <Lz> and <Sz>.
0,015 nm
0,2 s exposure

13.
Magnetic measurements with Atomic-Plane Resolution
Simulations
Example diffraction
pattern collected aside
an atomic plane
(d(110)/4) for Fe L3-edge.
For the preceding probe position,
sample thicknesses and
convergence semi-angles are
evaluated. 2 optimal combinations
are identified as (20,15) and
(30,10)
A 10 mrad probe semiangle is
therefore used to probe the non
magnetic signal.
The magnetic Signal is calculated
confirming the localization of the
APR-EMCD signal at positions ± d/4
distant from the lattice planes.

14.
• Fe (BCC) polycrystals
• 30 nm thickness
• 100 nm order of the lateral size of crystal grains
• 10 mrad beam convergence ADF
ADF smoothed profile
Spectra summation areas
Span based on local profile steepness.
Magnetic measurements with Atomic-Plane Resolution
Experiments
Rectangular acquisition area
necessary for data post-processing:
minimizes drift artifacts.
< 10 pixels acquired

15.
Magnetic measurements with Atomic-Plane Resolution
Data AnalysisEMCD spetras of one
region of interest:
Only few have neat
EMCD expected
signature. Some others
are noisy and others are
not expected.
CPD (Canonial
Poliadic
Decomposition)
data analysis is
performed,
revealing two
components.
Substraction of the
second CPD component
reveals more (50%)
EMCD like spectra,
removing false positives.
1st CPD component has
weak correlation with
ADF profile.
2nd comp. has strong correlation. A
channeling effect due to non-dipole
transitions is suggested.
Application of the Sum Rules yields
-0.1 < mL/mS < 0.3
<mL/mS>=0,057
In agreement with Fe expected values. However
Drift reduction si expected to notably reduce noise
and guarantee more reliability to the magnetic
ratio.

16.
Bibliography
[1] Schattschneider, Peter. Linear and Chiral Dichroism in the Electron Microscope. Singapore, Singapore: Pan Stanford Publishing Pte, 2012. Print.
[2] Stöhr, J., and Y. Wu. "X-Ray Magnetic Circular Dichroism: Basic Concepts and Theory for 3D Transition Metal Atoms." New Directions in Research with
Third-Generation Soft X-Ray Synchrotron Radiation Sources (1994): 221-50. Web.
[3] https://www-ssrl.slac.stanford.edu/stohr/xmcd.htm
[4] Schattschneider, P., S. Rubino, C. Hébert, J. Rusz, J. Kuneš, P. Novák, E. Carlino, M. Fabrizioli, G. Panaccione, and G. Rossi. "Detection of Magnetic
Circular Dichroism Using a Transmission Electron Microscope." Nature 441.7092 (2006): 486-88. Web.
[5] Rusz, Ján, Shunsuke Muto, Jakob Spiegelberg, Roman Adam, Kazuyoshi Tatsumi, Daniel E. Bürgler, Peter M. Oppeneer, and Claus M. Schneider.
"Magnetic Measurements with Atomic-plane Resolution." Nature Communications 7 (2016): 12672. Web.
[6] Schattschneider, P., S. Rubino, C. Hébert, J. Rusz, J. Kuneš, P. Novák, E. Carlino, M. Fabrizioli, G. Panaccione, and G. Rossi. "Detection of Magnetic
Circular Dichroism Using a Transmission Electron Microscope." Nature 441.7092 (2006): 486-88. Web.
[7] Rusz, Ján, Juan-Carlos Idrobo, and Somnath Bhowmick. "Achieving Atomic Resolution Magnetic Dichroism by Controlling the Phase Symmetry of an
Electron Probe." Phys. Rev. Lett. Physical Review Letters 113.14 (2014): n. pag. Web.
[8] Schattschneider, P., S. Löffler, M. Stöger-Pollach, and J. Verbeeck. "Is Magnetic Chiral Dichroism Feasible with Electron Vortices?" Ultramicroscopy 136
(2014): 81-85. Web.

17.
Thanks for Your
attention!