1. 2005 열역학 심포지엄
Experimental Evidence for Asymmetric Interfacial Mixing of Co-Al system
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
CMSEL
Hanyang Univ.

3. 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).
CMSEL
Hanyang Univ.
Simulation Results

4. Atomic deposition behavior
Al on Co(0001)
Co on Al(111)
TOP VIEW
CMSEL
Hanyang Univ.
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
It could be explained by the kinetic energy barrier for intermixing
CMSEL
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
CMSEL
Hanyang Univ.
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
CMSEL
Hanyang Univ.
Experimental Evidences

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

10. Atomic deposition behavior
Al on Co(0001)
CMSEL
Hanyang Univ.
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°)
CMSEL
Hanyang Univ.
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
CMSEL
Hanyang Univ.
Experimental Evidences

13. Conclusions
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Hanyang Univ.

14. Suggestion Magnetic Behavior of Co-Al system B2 - CoAl
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
CMSEL
Hanyang Univ.

15. Suggestion Co: Ferromagnetic CoAl: Nonmagnetic Co: Ferromagnetic
Al deposition
Co substrate
Al on Co substrate
Co: Ferromagnetic
GMR
structure
CoAl: Nonmagnetic
Co: Ferromagnetic
Active intermixing & Nonmagnetic B2-CoAl for Co on Al substrate
Sharp interface & Layer-by-layer growth of Al for Al on Co substrate
CMSEL
Hanyang Univ.

16. EAM potentials for Co-Al system
CoAl: B2
HCP - Co
B2 - CoAl
FCC - Al
Property
Co1)
CoAl(B2)2)
Al3)
Expt.
Calc.
a0 (Å)
2.507
2.512
2.86
2.867
4.05
4.049
Ecoh (eV)
4.39
4.29
4.45
4.468
3.36
3.39
B (GPa)
180
185
162
178 79
79.4
1) R. Pasianot et al. , PRB (1992).
2) C. Vailhe et al. J. Mater. Res., 12 No (1997).
3) A. Voter et al. MRS Symp.Proc. , 175 (1987).
CMSEL
Hanyang Univ.
Simulation Results