1. Co-Al 시스템의 비대칭적 혼합거동에 관한 이론 및 실험적 고찰
김상필1,2, 이승철1, 이광렬1, 정용재2
1. 한국과학기술연구원 미래기술연구본부
2. 한양대학교 세라믹공학과
박재영, 황정남
연세대학교 물리학과

2. Introduction Major Materials Issue is the interfacial structure
Typical structure of spintronic device
Major Materials Issue is the interfacial structure
and chemical diffusion in atomic scale
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3. Atomic deposition behavior
Al on Co(0001)
Co on Al(111)
TOP VIEW
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Simulation Results

4. Calculation Methods Simulation Results
Adatom (normal incident  0.1 eV)
300K Initial Temperature
300K Constant Temperature
Fixed Atom Position
Co-Al eam potential*
x,y-axis : Periodic Boundary Condition
z-axis : Open Surface
Deposition rate: × 10-1 nm/nsec
MD calc. step : 0.5fs
* C. Vailhe et al. J. Mater. Res., 12 No (1997).
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Simulation Results

5. Thin Film Growth Behavior
Atomic configurations
Layer density
3ML Al on Co(001)
No mixing
&
Sharp Interface
3ML Co on Al(001)
Mixing
&
Interface alloying
Significantly different thin film growth behavior was reported
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Hanyang Univ.
Simulation Results

6. Mixing Criteria Simulation Results Local Acceleration
Activation Barrier for Mixing
(1) Co Al
3.5eV
(2)
(3)
(4)
(1)
(2)
(4)
(3)
Reaction Coordinate
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Simulation Results

7. Ion Scattering Spectroscopy
CoAxial Impact Collision Ion Scattering Spectroscopy (CAICISS)
Energy range of ~ keV → penetration depth : < 10 Å
It can analyze the 3-dim. atomic structure of crystal surface and sub-surface by classical approximation of scattering
(bond direction)
intensity
(angle) Da o a c1 c2 a c1 d A B c2 o Da
Atomic geometry and shadow cone at various incident angles
Variation of intensity of ions
scattered by target atoms
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Experimental Evidences

8. Polar [1100]; clean Co(0001) surface×
Bridge site
On top site
hcp site
fcc site
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Experimental Evidences

9. Polar scan curves Experimental Evidences  along [1100] direction
Al atom(s)
1st Co layer
2nd Co layer
Ah2
fcc
hcp
On Top site(s)
Bridge
Ah2’, Af2’
Ah1’, Af1’
Ah1,,Af1
1.8 ± 0.05 Å
DFT calculation results
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Experimental Evidences

10. Atomic deposition behavior
Al on Co(0001)
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Simulation Results

11. Polar [100]; clean Al(001) surface
1st
2nd
3rd
4th
4.05 Å
A130
A132
A121
A11
A122
A123
A11 (12.9°)
A122 (11.52°)
A122 (26.4°)
A132 (20.4°)
A130 (79.1°)
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Experimental Evidences

12. Polar [100]: B2 structure Experimental Evidences
2nd Co
3rd
A130
A131
C230
C231
C232
4.05 Å
4th
2.867 Å
 B2-CoAl alloy was formed on Al(001) surface
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Experimental Evidences

13. Magnetic Behavior of Co-Al system
Stable intermetallic compound  B2(CsCl) structure
B2 - CoAl
Ab-initio calculations
Spin-Up
Spin-Down
FCC - Al
B2 - CoAl
HCP - Co
Nonmagnetic Metal
Nonmagnetic Metal
Magnetic Metal
 The perfectly ordered B2-CoAl does not show any magnetic behavior
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Simulation Results

14. (Magneto-Optic Kerr effects)
Experimental Measurement
Si substrate
Cu buffer layer (1500 A)
Co (30 A)
Al (30 A)
Al (840 A)
Capping layer (50 A)
Capping layer (50A)
MOKE
(Magneto-Optic Kerr effects)
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Experimental Evidences

15. Asymmetric Alloy EffectCo Al Al Co
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Experimental Evidences

16. Cap/Co/Buffer/Si(001) sample
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Experimental Evidences

17. Thickness of Mixing Region
~10 Å
Co: Ferromagnetic
GMR
structure
CoAl: Nonmagnetic
Co: Ferromagnetic
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Hanyang Univ.
Experimental Evidences

18. Conclusions Experimental Evidences Magnetic Behavior of CoAl
Deposition Behavior of Al on Co
Deposition Behavior of Co on Al
CMSEL
Hanyang Univ.
Experimental Evidences