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”
MANSE Midterm Review
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
MANSE Midterm Review
Organic Crystal Growth
Al doped 8-hydroxyquinoline
Physical vapor deposition
Alq3
Cu phthalocyanine (CuPc)
rubrene
MANSE Midterm Review
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.
MANSE Midterm Review
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
MANSE Midterm Review
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
MANSE Midterm Review
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)
MANSE Midterm Review
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
MANSE Midterm Review
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
MANSE Midterm Review
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
MANSE Midterm Review
-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
MANSE Midterm Review
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