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Probing Magnetic Nanostructures using Standing-Wave Excited Photoemission Spectroscopy and Microscopy. Alexander Gray University of California, Davis Materials Sciences Division, Lawrence Berkeley National Laboratory with.

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slide1

Probing Magnetic Nanostructures using Standing-Wave Excited Photoemission Spectroscopy and Microscopy

Alexander Gray

University of California, Davis

Materials Sciences Division, Lawrence Berkeley National Laboratory

with

C. Papp1,2,14, B. Balke1,2,13, S. Ueda3, K. Kobayashi3,4, F. Kronast5, M. Gorgoi5, R. Ovsyannikov5,

F. Schaefers5, S.-H. Yang6, L. Plucinski7, S. Döring8, U. Berges8, M. Huijben9,10, D. Buergler7, E. Rotenberg11, A. Bostwick11, B.C. Sell1,2,12, M. W. West2, M. Press2, F. Salmassi2,J.B. Kortright2, E. Gullikson2, S.S.P. Parkin6, W. Braun5, H. Dürr5, W. Eberhardt5, C. Westphal8, C.M. Schneider7,

R. Ramesh2,9, C. Felser14 and C.S. Fadley1,2

1Physics, UC Davis; 2Mat. Sci. Div., LBNL; 3SPring8; 4NIMS; 5HZB-BESSY Berlin; 6IBM Almaden; 7Research Center Jűlich; 8Physics, Tech. Univ. Dortmund; Physics; 9Mat. Sci., UC Berkeley; 10Univ. of Twente; 11ALS, LBNL;12 Pres. Add.--Physics, Otterbein Coll.; 13 Pres. Add.--Univ. Mainz, 14 Pres. Add.--Univ. Erlangen

Funded by the U.S. Department of Energy, under Contract No. DEAC02-05CH11231 and the Humboldt Foundation

Materials Science Division. Fadley Group.

slide2

Presentation Outline

  • Basic methodology
  • The La0.67Sr0.33MnO3/SrTiO3 Interface
    • Measurement Method
    • Measurement Results
    • Analysis
  • The MgO/Fe MTJ Interface on Multilayer Mirror
    • Measurement Method
    • Measurement Results
    • Analysis
  • Co Microdot Arrays on Multilayer Mirror
    • Measurement Method
    • Measurement Results
    • Analysis
  • Summary

8/20/2014

Materials Science Division. Fadley Group.

2

slide3

Measurement Technique

Standing-Wave Excited Photoemission

% modulation 

100 x 4R:

E.g. R = 5% 

90% modulation

R = 1% 

40% modulation

8/20/2014

Materials Science Division. Fadley Group.

3

slide4

La0.67Sr0.33MnO3/SrTiO3 Interface

La3d5/2 Resonance Peak and Reflectivity Measurements

8/20/2014

Materials Science Division. Fadley Group.

4

slide5

La0.67Sr0.33MnO3/SrTiO3 Interface

Rocking Curve Measurements and Simulations

Grazing Angle (Degrees)

Grazing Angle (Degrees)

hν = 833.2 eV

hν = 5956.4 eV

Exp.

Cal.

8/20/2014

Materials Science Division. Fadley Group.

5

slide6

La0.67Sr0.33MnO3/SrTiO3 Interface

Analysis Results

8/20/2014

Materials Science Division. Fadley Group.

6

slide7

La0.67Sr0.33MnO3/SrTiO3 Interface

Decreasing Thickness Profile

Bragg

Kiessig

Exp.

Cal.

hv = 833.2 eV

hv = 5956.4 eV

Sr3p 3/2

Sr3p 3/2

Thickness Gradient Profile

Ti2p 3/2

Ti2p 3/2

LSMO

STO

Substrate

Vacuum

BEST FIT

slide8

La0.67Sr0.33MnO3/SrTiO3 Interface

Constant Linear Thickness Profile

Exp.

Cal.

hv = 833.2 eV

hv = 5956.4 eV

Sr3p 3/2

Sr3p 3/2

Thickness Gradient Profile

Ti2p 3/2

Ti2p 3/2

LSMO

STO

Substrate

Vacuum

  • Amplitude of the Kiessig fringes does not agree with the experiment
  • Suppressed Kiessig fringes appear on both sides of the rocking curves
slide9

La0.67Sr0.33MnO3/SrTiO3 Interface

Increasing Thickness Profile

Exp.

Cal.

hv = 833.2 eV

hv = 5956.4 eV

Sr3p 3/2

Sr3p 3/2

Thickness Gradient Profile

Ti2p 3/2

Ti2p 3/2

LSMO

STO

Substrate

Vacuum

Kiessig fringes appear on the wrong side of the rocking curves

slide10

La0.67Sr0.33MnO3/SrTiO3 Interface

Decreasing Thickness Profile

Exp.

Cal.

hv = 833.2 eV

hv = 5956.4 eV

Sr3p 3/2

Sr3p 3/2

Thickness Gradient Profile

Ti2p 3/2

Ti2p 3/2

LSMO

STO

Substrate

Vacuum

BEST FIT

slide11

La0.67Sr0.33MnO3/SrTiO3 Interface

Analysis Results

LSMO

STO

8/20/2014

Materials Science Division. Fadley Group.

11

slide12

La0.67Sr0.33MnO3/SrTiO3 Interface

Mn3p Chemical Shift at the Interface

8/20/2014

Materials Science Division. Fadley Group.

12

slide13

La0.67Sr0.33MnO3/SrTiO3 Interface

Mn3p Chemical Shift at the Interface

Same interface effect is observed in a thicker multilayer (120 bilayers)

8/20/2014

Materials Science Division. Fadley Group.

13

slide14

Presentation Outline

  • Basic methodology
  • The La0.67Sr0.33MnO3/SrTiO3 Interface
    • Measurement Method
    • Measurement Results
    • Analysis
  • The MgO/Fe MTJ Interface on Multilayer Mirror
    • Measurement Method
    • Measurement Results
    • Analysis
  • Co Microdot Arrays on Multilayer Mirror
    • Measurement Method
    • Measurement Results
    • Analysis
  • Summary

8/20/2014

Materials Science Division. Fadley Group.

14

slide15

Measurement Technique

Standing-Wave Wedge Method

Photo-

Electron

Or Soft

X-ray

0.1 mm

spot

h =

0.5-6.0

keV

Buried

Interface

Bragg

Fixed phase

MgO

SW (|E2|) =

x/2sininc

 dML

Fe wedge

MFe

Scanned standing wave

Si

Mo

Multilayer

Mirror

1st order Bragg:

x =2dMLsinBragg

dML

dML

Si

Mo

SiO2

Scanned sample

6.0 mm

Si-wafer

With Yang, Parkin, Felser,…

8/20/2014

Materials Science Division. Fadley Group.

15

slide16

MgO/Fe Interface

Wedge San Fits

(b)

(a)

(d)

Al 2p

Mg 2p

Fe 3p

Expt.

YXRO

Calc.

R-factor analysis of the

concentration interface

(f)

(e)

O 1s

C 1s

8/20/2014

Materials Science Division. Fadley Group.

16

slide17

MgO/Fe Interface

MCD with Standing-Wave Excitation (hv = 900 eV)

[ILCP+IRCP]/2

Fe 2p3/2

ILCP

IRCP

Fe 2p1/2

Z Position

IMCD =

2[ILCP-IRCP]/[ILCP+IRCP]

IMCD

Z Position

8/20/2014

Materials Science Division. Fadley Group.

17

slide18

MgO/Fe Interface

MCD with Standing-Wave Excitation (hv = 900 eV)

R-factor analysis of the

magnetization interface

Fe 2p MCD

8/20/2014

Materials Science Division. Fadley Group.

18

slide19

MgO/Fe Interface

Analysis Results

Real sample: Concentration Profile

C/O ≈ 10 Å

Ideal growth recipe:

Al2O3 14 Å

2 Å diffusion

MgO 9 Å

4 Å diffusion

Fe wedge 0-200 Å

Atom-specific magnetization profile

MgO

9

Å

»

Winterf

4

Å

»

Wmagn

2.6

Å

-

Fe wedge 0

200

Å

8/20/2014

Materials Science Division. Fadley Group.

19

slide20

MgO/Fe Interface

SWedge Measurement Results

Self-consistent

X-ray optical

modeling of core

and valence PS

8/20/2014

Materials Science Division. Fadley Group.

20

slide21

Presentation Outline

  • Basic methodology
  • The La0.67Sr0.33MnO3/SrTiO3 Interface
    • Measurement Method
    • Measurement Results
    • Analysis
  • The MgO/Fe MTJ Interface on Multilayer Mirror
    • Measurement Method
    • Measurement Results
    • Analysis
  • Co Microdot Arrays on Multilayer Mirror
    • Measurement Method
    • Measurement Results
    • Analysis
  • Summary

8/20/2014

Materials Science Division. Fadley Group.

21

slide22

Cobalt Microdot Photoelectron Microscopy

Experimental Setup and Measured Sample

8/20/2014

Materials Science Division. Fadley Group.

22

slide23

Cobalt Microdot Photoelectron Microscopy

Photon Energy Rocking Curve Measurement Results: Al2p

8/20/2014

Materials Science Division. Fadley Group.

23

slide24

Cobalt Microdot Photoelectron Microscopy

Photon Energy Rocking Curve Measurement Results: C1s

8/20/2014

Materials Science Division. Fadley Group.

24

slide25

Cobalt Microdot Photoelectron Microscopy

Photon Energy Rocking Curve Measurement Results: Si2p

8/20/2014

Materials Science Division. Fadley Group.

25

slide26

Cobalt Microdot Photoelectron Microscopy

Photon Energy Rocking Curve Measurement Results: Co3p

8/20/2014

Materials Science Division. Fadley Group.

26

slide27

Cobalt Microdot Photoelectron Microscopy

Photon Energy Rocking Curve Measurement Results

8/20/2014

Materials Science Division. Fadley Group.

27

slide28

Summary

  • Photoelectron excitation with standing waves generated by reflection from multilayer mirror samples or substrates
  • Concentration profiles for constituent layers
  • Interface concentration profiles/average roughness
  • Element-specific magnetization profiles from MCD (MgO/Fe)
  • Complementary information from SX resonant and hard x-ray data, Bragg and Kiessig effects
  • Interface-specific core-level shifts (Mn in STO/LSMO)
  • Depth-resolved densities of states (MgO/Fe; STO/LSMO)
  • Depth-resolved photoelectron microscopy (Co microdots)

8/20/2014

Materials Science Division. Fadley Group.

28

slide29

Supporting Slides

8/20/2014

Materials Science Division. Fadley Group.

29

slide30

La0.67Sr0.33MnO3/SrTiO3 Interface

Mn3p Chemical Shift at the Interface

The interface chemical shift in Mn is observed in surface-sensitive soft x-ray data, but not in the bulk-sensitive hard x-ray data.

8/20/2014

Materials Science Division. Fadley Group.

30

sto and lsmo band structures

Expt’l. bandgap

3.3 eV = 0.24 Ry

STO and LSMO band structures

Empirical alignment of EF allows first 2-3 eV of LSMO bands to be seen (Kumigashira et al., J.A.P. 99, 08S903 (2006))

Zheng, Binggeli, J. Phys. Cond. Matt. 21, 115602 (2009)

Chikamatsu et al.,

PRB 73, 195105 (2006)

Mn eg

eg

Mn t2g

t2g

Mattheiss, PRB 6, 4718 (1972)

slide32

La0.67Sr0.33MnO3/SrTiO3 Interface

Valence Band Rocking Curve Measurements

The Mn eg and t2g peaks “rock” in-phase with the 3p peak

8/20/2014

Materials Science Division. Fadley Group.

32

slide33

La0.67Sr0.33MnO3/SrTiO3 Interface

ARPES

8/20/2014

Materials Science Division. Fadley Group.

33

slide34

Cobalt Microdot Photoelectron Microscopy

XMCD Microscopy

8/20/2014

Materials Science Division. Fadley Group.

34

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