Transcript MANSE Midterm Presen..

Organic Spintronics
Current team members
Franklyn Burke (graduate student, 2007-)
Huesyin Tokuc (graduate student, 2008-)
Prof. Greg Szulczewski
SFI Walton Fellow 2008-2009
“Spin Electronics with Organic Materials”
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Research Acitivities
• Growth of organic microcrystals and nanowires by
physical vapor deposition
• Characterization of organic wires by SEM, TEM, XRD,
PL, EPR, FT-IR, and SQUID magnetometery
• Fabrication of nanogap electrodes
• Set-up high impedance probe for magnetotransport
studies on crystalline organic semiconductors
• Construction of UHV chamber for spin valve growth
• Transport measurements on Alq3 based MTJs
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Organic Crystal Growth
Al doped 8-hydroxyquinoline
Physical vapor deposition
Alq3
Cu phthalocyanine (CuPc)
rubrene
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SQUID Magnetometery of Alq3
0.00018
Field -- 1T
Weight -- 63.2 mg
2
Magnetic moment,m-mo (10 Am )
0.00016
-3
0.00014
Al-doped
8-hydroxyquinoline
nanowires
0.00012
0.00010
0.00008
0.00006
0.00004
0.00002
0.00000
0
25
50
75
100 125 150 175 200 225 250 275 300
Temperature (K)
The concentration of paramagnetic (S= ½)
defect centers in Alq3 is estimated
to be: 4 x10-4/formula unit.
Unshaved material
scavenges Fe from the
stainless steel die!
This yield an average defect
separation of ~ 11 nm.
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Alignment of crystals on electrodes
Al-doped 8-hydroxquinoline
a = 24.936 Å, b = 28.551 Å, c = 3.787 Å
rubrene
a = 14.44 Å, b = 7.18 Å, c = 26.97 Å
Largest μ along B axis
Nano gap
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Fabrication of nano gap electrodes
UV optical lithography to prepare
Hall bar
Deposit Pt contacts on nanowire
by electron beam deposition
Focused–ion beam etching to
produce trench
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Magnetotransport in organic nanowires
Al-doped 8-hydroxyquinoline
NiFe electrodes
5T
Tunneling
50
200.0
180.0
1T
10 K
(x2)
140.0
VRH
120.0
300
20 K
(x10)
100.0
80.0
10K
40
200
0.5 T
30 K
0T
50 K
(x4)
R/R [%]
 (kOhms.cm)
160.0
4.2K
400
4.2 K
R/R [%]
220.0
Au electrodes
20K
30
30K
20
60.0
40.0
20.0
100
10
NNH
0.0
0
10 15 20 25 30 35 40 45 50
Temperature (K)
-4
-2
0
2
4
Magnetic Field (T)
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0
-5 -4 -3 -2 -1
0
1
2
3
Magnetic Field (T)
4
5
Rubrene crystals on NiFe electrodes
0.8
4.0E+06
0.7
Semiconducting
behavior
0.6
2
0.5
1
Current (A)
0.4
0.3
0
-1
70K
-2
0.2
-3
-10
0.1
-5
0
5
10
Voltage (V)
0.0
-0.1
70K
-0.2
75K
-0.3
80K
100K
-0.4
3.5E+06
3.0E+06
2.5E+06
2.0E+06
1.5E+06
150K
-0.5
1.0E+06
200K
-0.6
250K
-0.7
50
290K
100
-1.0
-0.8
-0.6
-0.4
-0.2
0.0
0.2
0.4
0.6
0.8
1.0
Voltage (V)
280nm gap
150
200
250
300
Temperature (K)
-0.8
Conductivity (Ohm-1 cm-1)
Current (A)
Resistance (Ohms)
3
8.E-07
7.E-07
6.E-07
5.E-07
4.E-07
σ = σo exp[-(TM/T)1/(1+d)
3.E-07
d =1 and TM ~ 235 K
2.E-07
50
100
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150
200
Temperature (K)
250
300
Magnetotransport for rubrene on NiFe
6
4.00x10
6
3.98x10
300nm gap
6
3.96x10
6
6
% MR
Resistance ()
3.94x10
3.92x10
6
3.90x10
70K
70 K
6
3.88x10
1V
6
3.86x10
6
3.84x10
6
3.82x10
-6
-5
-4
-3
-2
-1
0
1
2
3
4
5
6
5
4.5
4
3.5
3
2.5
2
1.5
1
0.5
0
MR proportional to T-2.25
50
Magnetic Field (T)
100
150
200
250
300
Temperature (K)
Negative MR scales linearly at high H
Negative MR is predicted to scale
as T-1.5 for 1D VRH*
Positive MR seen at low H
No MR observed using Au electrodes
*Nguyen et al. JETP 1985, 62, 1021
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TMR characteristics of 24 x 24μm2 junctions
The MTJ Stack: SiO2/Ta(30)/CoFe(5)/Barrier/CoFe(3)/IrMn(10)/Ta(5)/Pt(5)
10
54
10
52
8
51
6
50
4
49
162
160
8
158
6
156
154
4
152
2
2
150
48
0
-200 -150 -100
-50
0
50
100
150
200
148
0
47
250
-200 -150 -100 -50
H (Field (mT))
0
50
100 150 200
H (Field (mT))
20
14
18
13 K
AlOx
16
10
12
TMR (%)
TMR (%)
14
12
10
8
15 K
AlOx/Alq3
8
6
4
6
4
2
2
0
0
-1.0
-0.5
0.0
Voltage (V)
0.5
1.0
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-1.0
-0.5
0.0
Voltage (V)
0.5
1.0
146
Resistance (k)
53
Resistance (k)
12
TMR (%)
14
TMR (%)
2.5 nm Al2O3/ 1nm Alq3
2.5 nm Al2O3
On-going work
• Metal phthalocyanine (MPc) films
and crystal growth M= Mn, Fe, Co, Ni, Cu, and Zn
• Deposition of
vertical spin valves
in new UHV
chamber
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Future work
• Fabricate lateral spin valves with different
coercivity electrodes and gap separation
• Vertical spin valves with crystalline MPc’s
e.g. CoFe/MgO/MPc/LiF/Co
• Magnetometery, spectroscopy, and microscopy
of FM/organic and organic/FM interfaces
MANSE Midterm Review