Magnetic and Atomic Structures
Studied bySoft X-ray Spectroscopies

Kenta Amemiya (KEK-PF)

Outline
1. Magnetic structure (XMCD)
2. Surface and Interface(depth-resolved XAFS)
3. Future plans at a new soft X-ray beamline,
PF-BL-16A

Magnetic Structures Studied by
L/T Geometry Angle-dependent XMCDXMCD (X-ray Magnetic Circular Dichroism)
Element selectivity
Quantitative determination of spin & orbital
magnetic moments by using the sum rules

Transverse-B+B

Longitudinal
Angle-dependent XMCD⇒ Magnetic anisotropy
Separation of ms from mT

T. Koide et al., Rev. Sci. Instrum. 63, 1462 (1992).

Angle-dependent XMCD in Longitudinal (L) Geometry
T. Koide et al., Phys. Rev. Lett. 87, 257201 (2001)

Au/Co(2 ML)/Au(111)
Self-assembled Co islands
due to a reconstruction ofAu surface
All Co atoms are regarded to“interface” because of 2 MLthickness⇒ Direct observation ofinterface magnetism
Angle-dependent XMCD
⇒ Direct determination ofms, ml//, ml⊥, mT//, mT⊥

Sum rules in Longitudinal (L) geometry
Orbital sum rule (L geometry)-[ΔI L3 + ΔI L2 ]θ
I L3 + I L2θ
3 ⋅ morb=−4nh ⋅ μ B-Spin sum rule (L geometry)-[ΔI L3 − 2 ⋅ ΔI L2 ]θ
I L3 + I L2-=−(mspin + 7 ⋅ mTθ )2nh ⋅ μ B

B.T. Thole et al., PRL 68, 1943 (1992).
P. Carra et al., PRL 70, 694 (1993).

Angle-dependent XMCD Measurements
T. Koide et al., Phys. Rev. Lett. 87, 257201 (2001)

PF BL-11A

Angle dependence in XMCD
← Anisotropy in ml, mTmjθ = mj⊥cos2θ + mj∥sin2θ
(j = l or T)
mT⊥+ 2 mT∥= 0⇒ Determination of allmoments including
their anisotropy

Determined Magnetic Moments
T. Koide et al., Phys. Rev. Lett. 87, 257201 (2001)

Cluster-size dependent
phase transition

Angle-dependent Sum Rules

Orbitalsum ruleSpinsum rule// → Longitudinal⊥→ Transverse

Outline
1. Magnetic structure (XMCD)
2. Surface and Interface(depth-resolved XAFS)
3. Future plans at a new soft X-ray beamline,
PF-BL-16A

Principle of Depth-resolved XAFS (XMCD)
Surface

X-raysCircularly polarized
X-raysSamplee-Microchannel plateθdeAuger electronsPhosphor screen

eXMCD spectrum

CCD camerae- Surface sensitive
Electron yield XMCD measurements at different detection angles
A set of XMCD spectra with different probing depths

Feasibility Study: Magnetic Depth Profile of Fe/Cu(100)Amemiya et al., APL 84 (2004) 936.

3 ML FeoSur
faceSens

7 ML FeSu
rfaceitive(Normal Incidence, 130 K)

FeUniformoSe
nsitiveFe

Magnetization
Cu(100)Surface
Magnetization

Cu(100)Extraction of Surface and Interface XMCD spectra
Amemiya et al., PRB 72 (2005) 201404(R).

Interface (1 ML)
NiInner layers
Interface (1 ML)
Similar spectra forInterface and inner layers
Surface (1 ML)

Ni

Inner layers

Surface spectrum isdrastically different

Magnetic Structures at the Surface Amemiya et al., PRB 71 (2005) 214420.

mseff(surf) = 0.22ml(surf) = 0.10ml(surf)/ mseff(av) = 0.30

mseff(surf) = 0.36ml(surf) = 0.05
ml(surf)/ mseff(av) = 0.09

mseff(bulk) = 0.36ml(bulk) = 0.05ml(bulk)/ mseff(av) = 0.14

mseff(bulk) = 0.61ml(bulk) = 0.11ml(bulk)/ mseff(av) = 0.18Large in-plane surface orbital moment

Depth-resolved Observation of Atomic Structures
Co L-edge EXAFS

GrazingIncidence
Co (3 ML)/Ru(0001)

Intensity (arb. units)

3

1st (surface)
2nd3rd (interface)

Co

2

Ru
Depth dependenceof layer spacing

1800

900

1000

Photon Energy (eV)1100

Outline
1. Magnetic structure (XMCD)
2. Surface and Interface(depth-resolved XAFS)
3. Future plans at a new soft X-ray beamline,
PF-BL-16A

Soft X-ray Beamline BL-16A
Variable Polarization
Circular & Linear (vertical/horizontal)
Construction: Jun.-Oct. 2007
User Experiments: Oct. 2008

Expected Photon Flux at BL-16A

Photon Flux (photons/s)

L edges of
3d transition metals

M edges ofrare-earth elements

G1 (undulator: 1st)
E/ΔE = 4000
E/ΔE = 8000

1E12

G2 (1st)G2 (3rd)

1E11200

400

600

800

1000

1200

Photon Energy (eV)14001600

Experimental Facilities

X-ray Resonant
Magnetic Scattering

Three-dimensional
XAFS/XMCD

Angle-dependent XMCD(Superconducting magnet)

Depth-resolved XAFS/XMCD
XMCD-PEEM
Soft X-ray Holography

Resonant Magnetic Scattering

Commissioning from Oct. 2008
(T. Koide et al.)Observation of periodic structures in nm scale
Simultaneous determination of atomic and magnetic structures

PhotonDetector
SampleAperture(a) Perpendicular periodic structure(b) In-plane periodic structureThree-dimensional XAFS/XMCD
Commissioning from Nov. 2008
(Amemiya et al.)

X-ray Microbeam ＋ Depth Resolution ⇒ 3D micro XMCD(XAFS)

Imaging-type
Electron Detector
SurfaceInsensitiveeeeSurface
Sensitive

Three-dimensional information on
Atomic Structure (EXAFS)Electronic Structure (XANES)
Magnetic Structure (XMCD)Fast Polarization-Switching Project
Twin APPLE-II type undulators for fast polarization switching (~10 Hz)
e- orbital
to BL
Undulator I

Undulator II

Kicker magnet

T. Hara et al., J. Synchrotron Rad. 3, 426 (1998).
Y. Saitoh et al., J. Synchrotron Rad. 5, 542 (1998).

Lock-in technique ⇒ Observation of small (~10-4) dichroism
Undulator II will be installed in 2010

Detection of Small XMCD Signals
T. Koide et al., Phys. Rev. Lett. 87, 256404 (2001)

Observation of weak ferromagnetism

Precise investigation forphase transition phenomena

Summary
Angle-dependent L/T geometry XMCD

Depth-resolved XAFS/XMCD

Determination of ms, ml and mT
including their anisotropy

Atomic, electronic and magnetic
Structures at surface and interface
Circularly polarized
X-raysSampleMicrochannel plateθdPhosphor screen
CCD camera

Future plans
Resonant Magnetic Scattering Three-dimensional XAFS/XMCD Fast polarization switching
X-ray Microbeam＋ Depth Resolution ⇒3D micro XMCD(XAFS)
Imaging-type
Electron Detector

e- orbital

SurfaceInsensitive

PhotonDetector
SampleApertureeee
Surface
Sensitive

Undulator I
Kickermagnet

Undulator II

to
BL